Emerging Role of the Calcium-Activated, Small Conductance, SK3 K+ Channel in Distal Tubule Function: Regulation by TRPV4
Figure 6
Effect of TRPV4-mediated activation of SK3 channels on membrane potential, Vm.
A. Fluorescence image of a split-open CCD loaded with the voltage-sensitive fluorescence dye, DiSBAC2(3), showing loading of all cells. The fluorescence intensity is an index of Vm and is presented as relative fluorescence units (RFU). B. Effect of 50 mM K+ (High K+) application on Vm of CCD cells showing the expected membrane depolarization (increased RFU). C. Effect of 300 nM apamin or 50 nM IbTX application on Vm in basal conditions showing little or no effect of either apamin (Apa) or IbTX in the basal state (TRPV4 not activated). D. Effect of TRPV4 activation with GSK101 (50 nM) leading to membrane hyperpolarization of Vm (decreased RFU), as expected for SK3 and BK activation. Subsequent application of either 300 nM apamin or 50 nM IbTX now induce a marked depolarization of Vm (increased RFU) demonstrating inhibition of SK3 and BK, respectively. E. Summary graph showing mean changes in Vm in basal conditions upon addition of High K+ (High K+, n = 44 cells), 300 nM apamin, or 50 nM IbTX (Left panel, Basal). Right panel (GSK101: TRPV4 Activation) shows the results after activation of TRPV4 (Ca2+ influx). Both apamin and IbTX now bring about a significant depolarization of Vm (*P<0.01 compared to Basal). The combine addition of both apamin and IbTX (Apa + IbTX) displays an enhanced depolarization compared to addition of apamin or IbTX alone (**P<0.01). The number in parentheses is the number of cells for each group (n).