Genetic Ablation of Ca _V 3.2 Channels Enhances the Arterial Myogenic Response by Modulating the RyR-BK _Ca Axis

Abstract

Objective In resistance arteries, there is an emerging view that smooth muscle CaV3.2 channels restrain arterial constriction through a feedback response involving the large-conductance Ca2+-activated K+ channel (BKCa). Here, we used wild-type and CaV3.2 knockout (CaV3.2−/−) mice to definitively test whether CaV3.2 moderates myogenic tone in mesenteric arteries via the CaV3.2-ryanodine receptor-BKCa axis and whether this regulatory mechanism influences blood pressure regulation. Approach and Results Using pressurized vessel myography, CaV3.2−/− mesenteric arteries displayed enhanced myogenic constriction to pressure but similar K+-induced vasoconstriction compared with wild-type C57BL/6 arteries. Electrophysiological and myography experiments subsequently confirmed the inability of micromolar Ni2+, a CaV3.2 blocker, to either constrict arteries or suppress T-type currents in CaV3.2−/− smooth muscle cells. The frequency of BKCa-induced spontaneous transient outward K+ currents dropped in wild-type but not in knockout arterial smooth muscle cells upon the pharmacological suppression of CaV3.2 channel. Line scan analysis performed on en face arteries loaded with Fluo-4 revealed the presence of Ca2+ sparks in all arteries, with the subsequent application of Ni2+ only affecting wild-type arteries. Although CaV3.2 channel moderated myogenic constriction of resistance arteries, the blood pressure measurements of CaV3.2−/− and wild-type animals were similar. Conclusions Overall, our findings establish a negative feedback mechanism of the myogenic response in which CaV3.2 channel modulates downstream ryanodine receptor-BKCa to hyperpolarize and relax arteries.

T-type Ca2+channels and autoregulation of local blood flow

“…50 These results are generally in agreement with the hypothesis that pressure-dependent activation of Ca V 3.2 channels in the VSMC plasma membrane causes activation of Ca 2C sparks via Ryanodine receptors (RyRs) closely apposed to Sarcoplasmatic Reticulum (SR). This leads to activation of spontaneous transient outward currents (STOC) via BK Ca channels, and negative feedback on the cerebral myogenic tone, 63,105 as previously suggested for the involvement of Ca V 3.2 channels in relaxation of coronary arteries. 103 These effects of Ca V 3.2 channel deletion on myogenic tone were only observed in young mice (2-4 months) but not in mature adult mice (7-12 months) leading to the conclusion that Ca V 3.2 channel expression may protect against excessive tone and high blood pressure in young individuals.…”

“…This increase in myogenic tone following addition of Ni 2C was not seen in mesenteric arteries from Ca V 3.2 ¡/¡ mice. 50,63,105 The increased tone was mimicked by addition of the specific BK Ca channel blocker paxilline (1 mM) in rat cerebral arteries, 105 and this effect of paxilline was not seen in small mesenteric arteries from young Ca V 3.2-deficient mice. 50 These results are generally in agreement with the hypothesis that pressure-dependent activation of Ca V 3.2 channels in the VSMC plasma membrane causes activation of Ca 2C sparks via Ryanodine receptors (RyRs) closely apposed to Sarcoplasmatic Reticulum (SR).…”

“…50,63 This was shown to be dependent on generation of Ca 2C sparks via superficial SR ryanodine receptors causing activation of spontaneous transient outward currents via BK Ca channels and hyperpolarization to give negative feedback modulation on myogenic tone. 63 A potential role of Ca V 3.2 channels in protection of the myocardium against excessive arterial tone and age-dependent hypertension was indicated by the finding that the role of Ca V 3.2 channels in opposing myogenic tone found in young mice was completely absent in mature adult mice. 50 This protection could also be relevant in the kidney to protect glomerular capillaries as Ca V 3.2 deletion in mice resulted in an increased GFR.…”

“…60 Thus, the exact function of Ca V 3.1 and Ca V 3.2 channels in the resistance vasculature is currently under investigation using knockout mice. 46,50,[61][62][63][64] …”

Recent Advances in the Genetics of Atherothrombotic Disease and Its Determinants

“…99 Genetic ablation of CaV3.2 channels enhances the arterial myogenic response through modulation of the RyR-BKCa (ryodine receptors-large conductance Ca 2+ -activated K + channels) axis. 100 Conditional knockout of the E-twenty six factor Ets variant 2 in endothelial cells resulted in impaired neovascularization in response to ischemic tissue injury. 101 Mice lacking neuropilin-1 in cardiomyocytes and vascular smooth muscle cells exhibited decreased survival, because of development of cardiomyopathy and aggravated ischemia-induced heart failure.…”