K_ATPchannel conductance of descending vasa recta pericytes

Abstract

Using nystatin-perforated patch-clamp and whole cell recording, we tested the hypothesis that K(ATP) channels contribute to resting conductance of rat descending vasa recta (DVR) pericytes and are modulated by vasoconstrictors. The K(ATP) blocker glybenclamide (Glb; 10 microM) depolarized pericytes and inhibited outward currents of cells held at -40 mV. K(ATP) openers pinacidil (Pnc; 10 microM) and P-1075 (1 microM) hyperpolarized pericytes and transiently augmented outward currents. All effects of Pnc and P-1075 were fully reversed by Glb. Inward currents of pericytes held at -60 mV in symmetrical 140 mM K(+) were markedly augmented by Pnc and fully reversed by Glb. Ramp depolarizations in symmetrical K(+), performed in Pnc and Pnc + Glb, yielded a Pnc-induced, Glb-sensitive K(ATP) difference current that lacked rectification and reversed at 0 mV. Immunostaining identified both K(IR)6.1, K(IR)6.2 inward rectifier subunits and sulfonurea receptor subtype 2B. ANG II (1 and 10 nM) and endothelin-1 (10 nM) but not vasopressin (100 nM) significantly lowered holding current at -40 mV and abolished Pnc-stimulated outward currents. We conclude that DVR pericytes express K(ATP) channels that make a significant contribution to basal K(+) conductance and are inhibited by ANG II and endothelin-1.

Vasa recta pericytes express a strong inward rectifier K+ conductance

“…That conductance was reduced to 1.47 Ϯ 0.27 nS by the specific K ATP channel blocker glybenclamide (4). In this study, under similar conditions, at Ϫ60 mV, a Ba 2ϩ -sensitive current of Ϫ81 Ϯ 16 pA was found measured, representing a chord conductance of 1.35 Ϯ 0.3 nS.…”

“…Early evidence favored a dominant role for receptor-operated Ca 2ϩ entry into smooth muscle of efferent arterioles; however, it has recently been confirmed that voltage-gated Ca 2ϩ entry is important in juxtamedullary efferent arterioles and DVR pericytes (13,41). It has been confirmed that vasoconstriction of DVR by ANG II and endothelin I is accompanied by depolarization of the pericyte cell membrane through dual actions involving activation of a Ca 2ϩ -dependent Cl Ϫ channels (13,25,40) and inhibition of K ϩ conductance (4,24). The resulting shift in membrane potential toward the equilibrium potential of Cl Ϫ ion activates voltagegated Ca 2ϩ entry that can be inhibited by diltiazem (41) or nifedipine (39).…”

“…To minimize other K ϩ currents, the intracellular solution contained 3 mM ATP (to inhibit K ATP channels) and a low concentration of Ca 2ϩ (EGTA, 5 mmol/l, to minimize the activity of KCa channels). The extracellular solution also contained glybenclamide (10 mol/l) and niflumic acid (100 mol/l) to inhibit prominent conductances by K ATP and Ca 2ϩ -dependent Cl Ϫ channels, respectively (4,25). Whole cell membrane potential recording.…”

Membrane current oscillations in descending vasa recta pericytes

“…4). We previously showed that ANG II inhibits classes of K ϩ channels in DVR pericytes and it is possible that K Ca channels are suppressed as part of its action (5,34 ] CYT might also be favored by IP 3 R-and RyR-mediated leak of Ca 2ϩ into the cytoplasm to reach the CICR threshold. This sequence predicts that NSCC current will tend to fill SR stores even as Ca 2ϩ -ATPases and, possibly, Na ϩ /Ca 2ϩ exchange (NCX) are concomitantly clearing the cytoplasm of Ca 2ϩ .…”

“…We previously showed that stimulation of DVR pericytes by angiotensin II (ANG II) induces voltage-gated Ca 2ϩ entry and activates Ca 2ϩ -dependent chloride channels (ClCa) (35,49). High concentrations of ANG II (10 nmol/l) also inhibit K ϩ conductance so that the combination of CaCl activation and K ϩ channel suppression shifts the membrane potential toward the Cl Ϫ ion equilibrium potential (E Cl ) to depolarize the cells (5,34). A sizable fraction of DVR pericytes respond to ANG II stimulation with membrane potential oscillations.…”