Na/Ca exchangers in collecting cells of rat kidney. A single tubule fura-2 study.

Single pieces of fura-2-loaded cortical collecting tubule (CCT) isolated either from normal or adrenalectomized (ADX) rats were superfused in vitro, and the cytosolic calcium concentration [( Ca2+]i) was calculated from fluorescence recordings. The effects of altering the sodium gradient across cell membranes were investigated. Switching external sodium from 164 mM to 27 mM (low [Na+]o) had little effect on [Ca2+]i in normal tubules (106 +/- 9 versus 101 +/- 9 nM, n = 15) whereas it resulted in a large peak of [Ca2+]i in CCT from ADX-rats (270 +/- 32 versus 135 +/- 11 nM, n = 21). Since CCT from ADX rats are known to have a reduced Na-pump activity, the effect of ouabain treatment on CCT from normal rats was also tested. When CCT from normal rats were exposed to 1 mM of ouabain in the presence of 164 mM of [Na+]o, [Ca2+]i increased only moderately (123 +/- 15 versus 111 +/- 11 nM, n = 13); when the low [Na+]o solution was applied to these ouabain-treated tubules, a large and transient increase in [Ca2+]i was obtained (287 +/- 38 versus 123 +/- 15 nM, n = 13). This response was absent with [Ca2+]o = 0. The data suggest the presence of 3 Na+/1 Ca2+ exchangers in cell membranes of rat CCT.(ABSTRACT TRUNCATED AT 250 WORDS)