Renal Proximal Tubule Cells

Previous data suggested an active Clconductance in the renal proximal convoluted tubule, although single channel conductance and regulation were not found. We have investigated the presence and regulation of the C1channel in proximal convoluted tubules by patch clamp analysis. The current-voltage relationship of whole cells with 130 mM NaCI in the pipette was nonlinear. The addition of 1-34 PTH (10-8 M), forskolin, or cAMP significantly increased whole cell Clconductance. We found a single Clchannel in excised apical membranes possessing conductance of 33 picosiemens (pS) at positive and 22.5 pS at negative potential, which was blocked by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (10-i M) and was selective to Cl(Cl/Na = 10). The channel was activated by prolonged membrane depolarization, by a catalytic subunit of protein kinase A (PKA), or by purified kinase C (PKC), but not by Ca2" (1 pM) inside the membrane. During cell-attached patch clamping, the channel was similarly activated by PTH, phorbol ester, or dibutyryl cAMP in a dose-dependent manner. To investigate second messenger contributions to the PTH-action, the PTH-evoked channels were modified further by the subsequent addition of several blockers of the second messengers. This suggested that PKA and PKC were involved in Clchannel activation. We therefore conclude that renal proximal convoluted tubule cells possess an apical C1channel activated by PTH via the PKA and PKC pathways. (J. Clin. Invest. 1991. 88:735-742.)