Intracellular pH modulates the availability of vascular L-type Ca2+ channels.

Abstract

L-type Ca 2+ channel currents were recorded from myocytes isolated from bovine pial and porcine coronary arteries to study the influence of changes in intraceUular pH (pHi). Whole cell lca fell when pHi was made more acidic by substituting HEPES/NaOH with CO2/bicarbonate buffer (pHo 7.4, 36°C), and increased when pHi was made more alkaline by addition of 20 mM NH4C1. Peak/Ca was less pHi sensitive than late/ca (170 ms after depolarization to 0 mV). pHi-effects on single Ca ~+ channel currents were studied with 110 mM BaCI2 as the charge carrier (22°C, pHo 7.4). In cell-attached patches pHi was changed by extracellular NH4CI or through the opened cell. In inside-out patches pHi was controlled through the bath. Independent of the method used the following results were obtained: (a) Single channel conductance (24 pS) and life time of the open state were not influenced by pHi (between pHi 6 and 8.4). (b) Alkaline pHi increased and acidic pHi reduced the channel availability (frequency of nonblank sweeps). (c) Alkaline pHi increased and acidic pHi reduced the frequency of late channel re-openings. The effects are discussed in terms of a deprotonation (protonation) of cytosolic binding sites that favor (prevent) the shift of the channels from a sleepy to an available state. Changes of bath pHo mimicked the pHi effects within 20 s, suggesting that protons can rapidly permeate through the surface membrane of vascular smooth muscle cells. The role of pHi in Ca 2+ homeostases and vasotonus is discussed.

Splice Cassette II of Na+,HCO3− Cotransporter NBCn1 (slc4a7) Interacts with Calcineurin A

“…The comparison was made by a paired two-tailed Student's t test. D, net Na ϩ -dependent, EIPA-insensitive pH i recovery rates (n ϭ 6) after an NH 4 ϩ prepulse in the presence of 50 mM extracellular K ϩ . Buffering of intracellular Ca 2ϩ using BAPTA-AM significantly slowed down the rate of pH i recovery.…”

“…As recently reviewed in detail (41), both acute and sustained disturbances in VSMC pH i have pronounced effects on vasomotor function. Acute changes in pH i interfere with Ca 2ϩ homeostasis in VSMCs (42), which can likely be attributed to competition between the intracellular H ϩ and Ca 2ϩ for buffer binding (43,44) and possibly to altered ion channel function (3,4). Sustained changes in pH i affect VSMC contractions primarily by altering the Ca 2ϩ sensitivity of the contractile machinery (5, 8, 10).…”

“…A number of enzymes critical . B, net Na ϩ -dependent pH i recovery rate (n ϭ 6) measured after an NH 4 ϩ prepulse in the absence of CO 2 /HCO 3 Ϫ was unaffected by 10 M FK506. Experiments were performed in the presence of 50 mM extracellular K ϩ .…”

“…Because no effect of the calcineurin inhibitors was seen on intracellular buffering capacity, pH i recovery rates were calculated at similar pH i levels and compared directly. NH 4 Cl was initially washed out into a Na ϩ -free solution to measure the Na ϩ -independent pH i recovery rate. Subsequently, Na ϩ was returned to the bath solution, and the Na ϩ -dependent pH i recovery rate measured.…”

“…The need for cellular acid extrusion varies greatly under different physiological and pathological conditions, but in many cases the signaling pathways involved in regulating transporter activity are unknown. Functional consequences of disturbed pH i include changes in ion channel function (3,4) and intracellular enzyme activity (5,6).…”