Genistein potentiates the ANP effect on a K+-conductance in HEK-293 cells

HEK-293 cells are known to reflect many features of the late distal tubule. Furthermore, they have the ability to release urodilatin, the structural analog to AN P. RTPCR was performed to test for the expression of natriuretic peptide receptors. While the mRNA for the human ANP receptor (NPR-A, GC-A) could be amplified, the CNP-specific receptor NPR-B (GC-B) and the receptor specific for guanylins, GC-C, could not be detected. In patch clamp experiments the effects of ANP (10 nM) on membrane voltage (V-m) were monitored and HEK-293 cells depolarized by 2.3 +/- 0.5 mV (n = 14). In the presence of the EGF receptor blocker genistein (10 muM) the effect of ANP was increased by 65% to 3.9 +/- 0.8 mV (n = 14). After removal of genistein the ANP-mediated depolarization further increased by 147% to 5.7 +/- 1.0 mV (n = 14). ANP given repetitively without genistein had no increasing depolarizing effect in HEK-293 cells with time. The ANP effect could be fully blocked by 1 muM Ba2+ and by 1 muM of the specific PKG inhibitor KT5823 indicating that ANP inhibits a K+-conductance via a cGMP-dependent protein kinase. Genistein itself hyperpolarized the membrane voltage of HEK-293 cells by -3.9 +/- 0.6 mV (n = 11) and this effect could also be fully blocked by Ba2+ (-0.3 +/- 0.1 mV, n = 5), indicating that genistein activates a K+-conductance which contributes significantly to the membrane potential of HEK-293 cells. Copyright (C) 2003 S. Karger AG, Basel.