Ionic currents and endothelin signaling in smooth muscle cells from rat renal resistance arteries

Abstract

The repertoire of ionic channels expressed in myocytes freshly isolated from microdissected interlobar and arcuate arteries of rat kidney and their integrative behavior in response to endothelin-1 (ET-1) were studied by identification and characterization of major whole cell current components using patch-clamp technique. In renal microvascular smooth muscle cells (RMSMC) dialyzed with K(+)-containing solution, rapidly inactivating (Ito) and sustained outward K+ currents were identified. Voltage-dependent Ito was categorized as "A" current based on its kinetics, sensitivity to 4-aminopyridine (4-AP), and refractoriness to tetraethylammonium (TEA+). Ca(2+)-activated component of K+ current was completely blocked by 10 mM TEA+, whereas 5 mM 4-AP did not affect this current. Maximal Ca2+ current (ICa) recorded in Cs(+)-loaded RMSMC reached 250 pA when cells were bathed in a solution with 2.5 mM Ca2+. Two patterns of ICa differing in kinetics, voltage range of activation and inactivation, and sensitivity to nifedipine were identified as T and L currents. Ca(2+)-dependent current component showing reversal potential near Cl- current (ECl) and sensitivity to blocking action of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid was identified as Ca(2+)-activated ECl. Activation of RMSMC with ET-1 (1-10 nM) induced elevation of [Ca2+]i and subsequent activation of Ca(2+)-activated ICl, which led to membrane depolarization sufficient to activate voltage-gated Ca2+ channels. ET-1-evoked transient reduction of ICa carried through voltage-gated Ca2+ channels was followed by augmentation of L-type ICa. ET-1-induced mobilization of intracellular Ca2+, accompanied by membrane depolarization, resulted in activation of Ca(2+)-dependent K+ channels, which can play the role of a feedback element terminating ET-1-induced membrane depolarization.

Cellular mechanisms mediating rat renal microvascular constriction by angiotensin II.

“…Collectively, our findings suggest that in afferent arterioles, phospholipase C-dependent calcium release from endoplasmic reticulum (35) triggers subsequent cellular responses that activate voltage-dependent calcium channels. Electrophysiological studies indicate the presence of calcium-activated chloride channels on preglomerular vessels, including afferent arterioles (10,36). Furthermore, previous data demonstrated that chloride channel blockade inhibited AngII-induced afferent arteriolar constriction (11,37).…”

Cytochrome P450 and Cyclooxygenase Metabolites Contribute to the Endothelin-1 Afferent Arteriolar Vasoconstrictor and Calcium Responses

“…Second messengers responsible for the ET-1-mediated vascular response include phospholipase C activation and subsequent calcium mobilization from intracellular stores, as well as phospholipase A 2 stimulation, resulting in production of arachidonic acid metabolites. 1,14,21,25 In freshly isolated smooth muscle cells from large-caliber renal vessels, Gordienko et al 25 demonstrated that ET-1-induced mobilization of intracellular calcium was accompanied by membrane depolarization. ET-1 also stimulated Ca 2ϩ -activated K ϩ channels in renal vascular smooth muscle cells.…”

Molecular Physiology of Low-Voltage-Activated T-type Calcium Channels

“…In guinea pig smooth muscle myocytes, endothelin stimulated the activity of a 12-pS channel, that may or may not be carried through T-type channels (181). Endothelin has been reported to have no effect on T-type currents recorded from smooth muscle cells from rat renal resistance arteries (143).…”

“…T-type currents have only been recorded from smooth muscle cells (SMC) isolated from rat interlobular and arcuate arteries (143). Heterogeneity in Ca 2ϩ currents was observed, with approximately one-third of the freshly isolated myocytes displaying only T-type currents ("T-rich"), one-third only L type, and the rest a mixture.…”