Mechanosensitive ion channels in skeletal muscle from normal and dystrophic mice.

Abstract

1. We examined the activity of single mechanosensitive ion channels in recordings from cell-attached patches on myoblasts, differentiated myotubes and acutely isolated skeletal muscle fibres from wild-type and mdx and dy mutant mice. The experiments were concerned with the role of these channels in the pathophysiology of muscular dystrophy. 2. The predominant form of channel activity recorded with physiological saline in the patch electrode arose from an -25 pS mechanosensitive ion channel. Channel activity was similar in undifferentiated myoblasts isolated from all three strains of mice. By contrast, channel activity in mdx myotubes was -3-4 times greater than in either wildtype or dy myotubes and arose from a novel mode of mechanosensitive gating. 3. Single mechanosensitive channels in acutely isolated flexor digitorum brevis fibres had properties indistinguishable from those of muscle cells grown in tissue culture. The channel open probability in mdx fibres was -2 times greater than the activity recorded from wild-type fibres. The overall level of activity in fibres, however, was roughly an order of magnitude smaller than in myoblasts or myotubes. 4. Histological examination of the flexor digitorum brevis fibres from mdx mice showed no evidence of myonecrosis or regenerating fibres, suggesting that the elevated channel activity in dystrophin-deficient muscle precedes the onset of fibre degeneration. 5. An early step in the dystrophic process of the mdx mouse, which leads to pathophysiological Ca2+ entry, may be an alteration in the mechanisms that regulate mechanosensitive ion channel activity.

Maturation and myotonia influence the abundance of cation channels K DR , K IR and C IR differently: a patch-clamp study on mouse interosseus muscle fibres

“…With respect to conductance and kinetics, C IR resembles mechanosensitive cation channels, a low resting activity of which has been demonstrated in muscle fibres of young mice [11]. Systematic application of pressure was not possible with our recording equipment, but there was no indication of sensitivity to membrane deformation.…”

Utrophin suppresses low frequency oscillations and coupled gating of mechanosensitive ion channels in dystrophic skeletal muscle

“…Patch electrodes were pulled from borosilicate capillaries and the tips heat polished to give a final resistance of »1.5 -1.7 MV with the electrode filled with normal saline and immersed in bathing solution containing isotonic K C -aspartate. 15,16,23 The electrode solution contained (in millimolar): 150 NaCl, 5 KCl, 1 MgCl 2 , 10 EGTA, 10 HEPES, and 17 glucose. The bathing solution contained (in millimolar): 150 potassium aspartate, 5 MgCl 2 , 10 EGTA, 10 HEPES, and 10 glucose.…”

“…Methods for isolating single flexor digitorum brevis (FDB) muscle fibers were identical to those described in previous studies. 15,23,35 Dissociated fibers were incubated in oxygenated culture media at 34 C prior to use.…”

“…There is now strong evidence showing mechanosensitive (MS) ion channels contribute to pathological Ca 2C entry in dystrophic skeletal muscle. [14][15][16][17][18][19][20][21][22][23] Recent work suggests MS channels in skeletal muscle are formed from TRPV4 proteins, although the precise subunit composition remains to be determined. 24 The mechanisms by which MS channels transduce mechanical forces in skeletal muscle are only beginning to be understood.…”

“…MS channel activity appears as short bursts of openings separated by longer closed periods. 15,23 The short horizontal bar at the top of the first record in Figure 1a indicates the burst of single-channel activity shown at the bottom on an expanded time scale. Single MS channel activity appears as rapid opening and closings with excursions to distinct subconductance levels.…”