A voltage‐dependent proton current in cultured human skeletal muscle myotubes.

Abstract

SUMMARY1. A voltage-dependent proton current, IH' was studied in cultured myotubes obtained from biopsies of human muscle, using whole-cell recording with the patchclamp technique.2. With a pH. of 8-0 and a calculated pHi of 6-3, IH was activated at voltages more depolarized than -50 mV and its conductance reached its maximum value at voltages more depolarized than + 10 mV.3. Studies of the reversal potential ofIH during substitution of K+, Na+, Ca2+, Cl-, Cs+ and H+ in the extracellular solution indicated that protons were the major charge carriers of IH 4. IH was also activated during a voltage step to + 22 mV with a pHo of 7-3 and a calculated pHi of 7-3. 5. Acidification of the extracellular solution led to a shift towards depolarized voltages of the conductance-voltage relationship.6. Stationary noise analysis ofIH suggested that the elementary event underlyingIH was very small with a conductance of less than 0 09 pS.7. Extracellular application of various divalent cations blocked IH. The block by divalent cations was voltage dependent, being more efficient at hyperpolarized than at depolarized voltages. For Cd2 , the Michaelis-Menten constant (Km) for the block was 0-6 ,tM at -28 mV and 10-4 #4M at + 12 mV.8. Ca2+ was a less efficient blocker than Cd2+ but could block IH at physiological concentrations (the Km values for the block were 0 9 mm at -38 mV and 7-3 mm at -8 mV).9

Voltage‐Gated Proton Channels

“…In 1993, proton currents were recorded in three human cell types (24, 76), including human neutrophils (63), confirming the hypothesis of Henderson and colleagues. The number of cell types reported to express proton channels continued to expand.…”

Needle muscle biopsy in the investigation of neuromuscular disorders

“…The possibility of controlling the degree of maturation of cultured human muscle cells using different culture media 11,18 and the possibility of identifying and purifying human muscle satellite cells immediately after dissociation of a muscle biopsy 1 have opened new perspectives. It is now possible to study physiological and physiopathological properties of satellite cells 2,12 and of their progeny 3,4,15 in pure cultures that are not ''contaminated'' by nonmuscle cells. In view of this, the method described here for recovering satellite cells from fine NMB should be useful for the exploration of various aspects of muscle disorders in cell culture.…”

pH regulation and beyond: unanticipated functions for the voltage-gated proton channel, HVCN1

“…In 2006, human HVCN1 was cloned [5], as were homologous genes in mice and Ciona intestinalis [9]. The human HVCN1 (Figure 1) is expressed in two isoforms, the full-length protein (273 amino acids), and a short form, which lacks the first 20 amino acids, thus far documented only in B cells [26].…”

“…Proton currents were identified in snail neurons and amphibian oocytes in the 1980s [1–3], in mammalian cells in 1991 [4], and in human cells in 1993 [5–7]. However, the gene encoding the channel was not discovered until 2006 when two groups cloned human and murine HVCN1 genes [8, 9], prompting a wave of new studies on voltage-gated proton channel function and regulation.…”