Abstract
Abstract: :
Purpose: To measure the electrical properties of the bovine lens given indications that the distribution of its transport elements (1) varies from that of the rabbit lens (2). Methods: Bovine lenses were isolated in a modified Ussing–type chamber (2) within 1 hr of the death of the animal at a local slaughterhouse. The 17–19 mm–diameter lens was seated posterior–side down upon a greased 12 mm–diameter O–ring, and rigidly held in place by a small hydrostatic pressure difference, which enabled a tight electrical seal and exposed about 95% of the lens surface area to the bathing media. The translens potential difference (PDt) was measured between the posterior–side bath (which contained the reference electrode) and the anterior–side, within which the anterior–plus–equatorial surfaces were bathed. Results: Under the above conditions, PDt was either a few mV positive (0.5 to 4 mV) or negative (–0.3 to –5 mV) with respect to the posterior bath (n= 20 lenses). In one set of experiments in which the effects of the bilateral additions of the K channel blocker, quinidine (0.2 mM), were recorded, the control PDt was –3.7 ± 1.3 mV (n= 7). The addition of quinidine to the posterior–side bath increased PDt to 3.7 ± 0.5, which was in turn reduced to 2.0 ± 0.4 mV upon addition of the blocker to the anterior bath. PDt was then rapidly reduced to 1.0 ± 0.5 upon the introduction of ouabain to the anterior side. The Na,K pump–current inhibitor was ineffective when added to the posterior side. In a second set of experiments under Cl–free conditions, baseline PDt was 1.4 ± 0.3 mV (n= 4). It was increased to 2.2 ± 0.2 and decreased to 1.5 ± 0.1 on adding quinidine to the posterior and anterior sides respectively. Ouabain was then added to reduce the PD to 0.3 ± 0.2 mV (n= 4). Conclusions: Bovine PDt is the result of a balance of EMF's created by a tendency of K diffusion from lens–to–bath anteriorly and posteriorly plus a ouabain–inhibitable Na,K pump–current across the anterior surface only. When the anterior side was negative, the K EMF of the posterior side was larger than the combined EMF’s of the anterior K conductances plus Na,K pump–current. The presence or absence of Cl did not determine whether or not the anterior side was negative with respect to the posterior. Overall, these results indicate a distribution of ionic channels around the surface of the bovine lens that seems to differ from that previously described for the rabbit lens (2). (1) Delamere & Duncan. J Physiol, 1979, 295: 241–9. (2) Candia & Zamudio. Am J Physiol, 2002, 282: C252–62.
Keywords: ion channels • ion transporters • NaK ATPase