Z. Zellforsch. 131, 199--203 (1972) © by Springer-Verlag 1972

Tight Junctions in the Stratum basale of Ruminal Epithelium

A. Scott , I sobel C. Gardner , D. P~. Fu l ton , and C-. B. McInroy

Department of Biology, University of Strathclyde, Glasgow, Scotland

t~eceived March 6, 1972

Summary. Occluding junctions, conforming to the descriptions of Farquhar and Palade, have been found to occur in the stratum basale of ruminal epithelium. The junctions, which are located deep on the plasma membranes in cells both from the rumen and the omasum, have measurements which fall well within the range given by Henrikson.

Key words: Tight junctions - - Ruminal epithelium - -St ra tum basale - - Sheep.

Introduction

Considerable in te res t r ecen t ly has centred on the occurrence and d is t r ibu t ion of t igh t junc t ions in rumina l epi thel ium. Differences of opinion have ar isen as to whether these occluding junct ions are zonulae or maculae and whe the r t hey occur t h roughou t the ep i the l ium or are res t r ic ted to the ou te rmos t s t ra ta , t t en- r ikson (1970), Steven and Marshal l (1970) and more recen t ly Schnorr and Wille (1972) have each discussed t igh t junct ions in rnmina l ep i the l ium with special reference to thei r role as barr iers to the backward diffusion of metabol i t es to the lumen of the rumen from the in terce l lu lar spaces, and in most cases have presented evidence for the i r occurrence in the stratum granu losum- - s t ra tum corneum region. The f irst two au thors add i t i ona l ly s ta te t h a t occluding junc t ions are also to be found th roughou t the other s t r a t a of the epi thel ium, bu t ne i ther has presented convincing evidence to suppor t these s ta tements .

The purpose of this shor t paper is to provide conclusive evidence t h a t occluding junct ions, which conform to the descr ipt ions of F a r q u h a r and Pa lade (1965), do occur in the stratum basale of rumina l epi thel ium.

Materials and Methods Papillae were removed from the region of the ventral sac of the rumen and from the

omasal lamina of a sheep, cut into small pieces and fixed for 4 hours in 5% glutaraldehyde buffered with cacodylate at pH 7.2. The tissue was post-fixed in osmium, dehydrated by passage through a graded series of alcohols and embedded in Araldite (TAAB Labs.). Sections were cut on an LKB Ultratome I I I and, after staining in uranyl acBtate and in Reynold's lead citrate, were viewed in an A.E.I. EM 6B.

Results and Discussion The widespread d i s t r ibu t ion of desmosomes or maculae adhaerentes in rumina l

ep i the l ium is well known: the p rob lem would appea r to arise wi th the occluding junct ions bo th wi th respect to thei r na tu re and thei r d is t r ibut ion , t t en r ikson

A. Scott, I. C. Gardner, D. R. Fulton and G. B. McInroy: 200

Fig. 1. Base of the omasal epithelium to show the position of an occluding junction (arrowed). The junction in part is shown at greater magnification in the inset where the median dense band is clearly visible. The dense band measures 38/~ across and the fused membranes 213 A.

×47000. Inset ×211000

Fig. 2. An occluding junction (arrowed) between adjacent cells in the stratum basale of rumen epithelium. The basal membrane with underlying collagenous fibres are evident. × 16000

(1970a, b) and Henr ikson and S tacy (1971) s ta te t h a t maculae b u t no t zonulae occludentes are seen in the epi the l ium, while S teven and Marshal l (1970) descr ibe bo th zonulae and maculae. The zonulae were shown to occur in the stratum granu- losum jus t below the junc t ion wi th the stratum corneum while the maculae were r epo r t ed to be found in the stratum basale and the stratum spinosum. More recen t ly Sehnorr and Wil le (1972) con tend t h a t zonulae are presen t in the stratum eorneum of goa t epi the l ium.

The associa t ion be tween occluding junct ions and the p rox ima l regions of the epi the l ium, i.e. wi th the t o p m o s t stratum granulosum and the stratum corneum,

Tight Junctions in the Stratum basale of Ruminal Epithelium 201

Fig. 3. The occluding junction from Fig. 2 further magnified to show the median dense band (width 36 A) and the fused membranes (width 230 A). The junction has a length of 0.9tz.

A desmosome is visible on the left of the figure. × 56000

would point to distinct similarities in physiological ultrastructure between ruminal epithelium and the epidermis of the frog (Farquhar and Palade, 1965) and it is perhaps for this reason that so much attention has been given to occluding junctions in this region.

The occluding junctions occur towards the base of the cells in both the rumen and the omasum, not far distant from the basal membrane with its hemidesmo- somes. The position of such a junction between omasal epithelial cells can be seen in Fig. 1, while Fig. 2 shows the same for ruminal cells. This last junction has been magnified to show more clearly the arrangement of the membranes (Fig. 3). Here the outer leaflets of the membranes have converged to form a single distinct dense band approximately 36 ~ thick. The two membranes fused measure 230 A across and the extent of the area of fusion is 0.9 ix. Another tight junction, again from cells in the basal region of the rumen, is shown in Fig. 4: here the leaflets of the cell membranes can actually be seen to converge giving rise to the median dense band. The intercellular space, formed when the outer leaflets separate again was found to have a width in the region of 320 A in the junctions examined--a figure comparable with that given for frog skin (Farquhar and Paladc, 1965). The measurements for the median dense band thickness at this particular junction agrees with that given above : the fused membranes, however,

Fig. 4. Another t ight junction of total length 0.96 ~z from cells in the basal region of the rumen. The fused membranes and the median dense band have widths of 190 and 32 ~ respectively. Desmosomes (D) are present on either side of the junction and tonofilaments (T) can be seen

in the cytoplasm, x 108000

A. Scott et al.: Tight Junctions in the Stratum basale of Ruminal Epithelium 203

are less th ick by some 40 A while the t o t a l length of m e m b r a n e fusion is grea ter b y 600 A. Desmosomes are visible a t shor t d is tances f rom the po in ts of conver- gence of the membranes and bundles of tonof i laments a r ranged para l le l to the p l a sma m e m b r a n e - - a fea ture character is t ic of cells f rom this r e g i o n - - a r e also clear ly visible.

The lengths given above for the junct ions measured compare f avourab ly with the m a x i m u m length of 1 ~ found by Henr ikson (1970). I t has not been possible to compare our dimensions wi th those of S teven and Marshal l (1970) since none are given in the t ex t and no micrographs of junct ions in the stratum basale are presen t f rom which measurements can be taken . No dimensions for occluding junct ions in th is region of ruminM epi the l ium have been found in the l i te ra ture .

We are no t in a pos i t ion f rom the presen t work to conclude whe ther the occluding junct ions which we f ind in the basal layer are zonulae or maculae occlu- dentes withou t fur ther serial sect ioning and, in addi t ion , sect ioning the ma te r i a l in different planes. I t is for this reason therefore, t h a t we have prefer red to use the t e rm "occ lud ing j u n c t i o n " in this paper r a the r t han be more specific a t th is stage.

References Farquhar, M. G., Palade, G. E. : Cell junctions in amphibian skin. J. Cell Biol. 26, 263-291

(1965). Henrikson, 1%. C. : Ruminal epithelium : transport of solutes in the absence of tight junctions

(zonulae occludentes). J. Anat. (Lond.) 106, 199 (1970a). Henrikson, R. C. : Ultrastructure of ovine ruminal epithelium and localisation of sodium in

the tissue. J. Ultrastruct. Res. 30, 385401 (1970b). Henrikson, R. C., Stacy, B. D. : A barrier to diffusion across ruminM epithelium: A study by

EM using horseradish peroxidase, lanthanum and ferritin. J. Ultrastruct. l~es. 34, 72-82 (1971).

Schnorr, B., Wille, K.-H. : Zonulae occludentes im Pansenepithel der Ziege. Z. Zellforseh. 124 39-43 (1972).

Steven, D. H., Marshall, A. B. : 0rganisation of the rumen epithelium. In: Phillipson, A. T. (ed.): Physiology of digestion and metabolism in the ruminant. Proc. 3rd. Internat. Sympos. Cambridge, August 1969; Newcastle upon Tyne: Oriel 1970.

Dr. A. Scott, Dr. I. C. Gardner Department of Biology University of Strathclyde Glasgow, C.I., Scotland