Acidic regulation of junction channels between glomus cells in the rat carotid body. Possible role of [Ca(2+)](i)

Abstract

The purpose of this work was to characterize the gap junctions between cultured glomus cells of the rat carotid body and to assess the effects of acidity and accompanying changes in [Ca(2+)](i) on electric coupling. Dual voltage clamping of coupled glomus cells showed a mean macrojunctional conductance (G(j)) of 1.16 nS+/-0.6 (S.E.), range 0.15-4.86 nS. At normal pH(o) (7.43), a steady transjunctional voltage (DeltaV(j)=100.1+/-10.9 mV) showed multiple junction channel activity with a mean microconductance (g(j)) of 93.98+/-0.6 pS, range 0.3-324.5 pS. Single-channel conductances, calculated as variance/mean g(j), gave a mean value of 16.7+/-0.2 pS, range 5.13-39.38 pS. Manual measurements of single-channel activity showed a mean g(j) of 22.03+/-0.2 pS, range 1.3-160 pS. Computer analysis of the noise spectral density distribution gave a channel mean open time of 12.7+/-1.5 ms, range 6.37-23.42 ms. The number of junction channels, estimated in each experiment from G(j)/single-channel g(j), showed a range of 7 to 258 channels (mean, 107.2). Optical measurements of [Ca(2+)](i) gave a mean value of 80.2+/-4.27 nM at pH(o) of 7.43. Acidification of the medium with lactic acid (1 mM, pH 6.3) induced: 1) Variable changes in G(j) (decreases and increases); 2) A significant decrease in mean g(j) (to 80.36+/-0.34 pS) and in single-channel conductance (g(j)=12.8+/-0.2 pS in computer analyses and 17.23+/-0.2 pS when measured by hand); 3) Variable changes in open times, resulting in a similar mean (12.8+/-1.5 ms) and 4) No change in the number of junction channels. When pH(o) was lowered to 6.3 [Ca(2+)](i) did not change significantly (there were increases and decreases). However, when pH(o) was lowered to 4.4, [Ca(2+)](i) increased significantly to 157.1+/-8.1 nM. It is concluded that saline acidification to pH 6.3 depresses the conductance of junction channels and this effect may be either a direct effect on channel proteins or synergistically enhanced by increases in [Ca(2+)](i). However, there are no studies correlating changes of [Ca(2+)](i) and intercellular coupling in glomus cells. Stronger acidification (pH(o) 4.4), producing much larger changes in [Ca(2+)](i), may enhance this synergism. But, again, there are no studies correlating these effects.