Renal Vascular Kv and Ca2+ Channel Alterations in the SHR are Dependent on Protein Kinase C Activity
It is well established that in renal vascular smooth muscle cells of the SHR there is membrane depolarization, a decrease in Kv current and an increase in Ca2+ current when compared to control WKY cells. It is also well accepted that protein kinase C (PKC) activity in SHR vascular smooth muscle is increased when compared to the WKY vasculature. The objective of this study was to investigate if the increased vascular PKC activity of the SHR plays a role in the regulation of SHR renal smooth muscle cell Kv and Ca2+ channels. Basal PKC activity was increased ∼3-fold in the SHR renal arterioles when compared to the WKY (2.2±0.4 vs 6.3±0.6 nmol[32P]/min/mg protein, n=7, P≤0.01). Western blot analysis showed the presence of four different PKC isoforms, α, δ, ε and ζ, in both WKY and SHR renal resistance arterioles. Of the four isoforms, only the levels of PKC-α and ε were significantly increased in the SHR when compared to the WKY. To investigate the influence of PKC on vascular membrane potential, Kv and Ca2+ current, renal resistance arteriolar cells were treated with PKC inhibitors (staurosporine or Calphostin C,1 μM) or activators (PMA or PDBu, 100 nM) for 1 hour and then subjected to whole cell patch clamp analysis. Interestingly, when SHR renal smooth muscle cells were treated with either PKC inhibitor, the membrane depolarization, decrease in Kv current and increase in Ca2+current usually observed were abolished, i.e. the SHR cells electrophysiologically resemble WKY cells. When WKY renal smooth muscle cells were treated with either phorbol ester, they caused membrane depolarization (22±3.5 mV, n=8), a decrease in Kv current (65±8.5%, n=10) and an increase in Ca2+ current (125±11%, n=9), i.e. WKY cells electrophysiologically resemble SHR cells. These data suggest, that in renal arterioles of the SHR, increased PKC activity plays a role in the regulation of Kv and Ca2+ channels, which in turn alters membrane potential, intracellular free Ca2+ concentration and the resting tone of vascular smooth muscle in the kidney. This then would further decrease renal blood flow and exacerbate the hypertensive state.