The effects of pH on Ca2+-activated force in frog skeletal muscle fibers

Abstract

Ca2+-activated isometric force was recorded is skinned (sarcolemma mechanically removed) segments of frog skeletal muscle fibers immersed in bathing solution of different pH (5.0--10.5) and Ca2+ concentrations. Force in maximally activated fibers was near zero at pH 5.5, increased as pH increased to 7.5, remained relatively constant until pH 9.0 and then rapidly declined to zero by pH 10.5. The Ca2+ concentration at which 50% of maximum force was developed decreased 25-fold as pH increased from 5.5--7.5. The data also indicate that, while the fibers remains viable with acidosis, they deteriorate rapidly with alkalosis. These observations may be relevant clinically, since they parallel known effects of acidosis on cardiac contractility. The possible sites of action of H+ on the Ca2+-activated force generating mechanisms are discussed.

Effect of pH on the rate of myosin head detachment in molluscan catch muscle: are myosin heads involved in the catch state?

“…Effects of pH on contractile properties were also found on other muscles. In skinned cardiac and skeletal muscle preparations, a moderate alkalisation produced an increase of maximum tension and Ca 2+ sensitivity (Ashley and Moisescu, 1977;Fabiato and Fabiato, 1978;Robertson and Kerrick, 1979;Chase and Kushmerick, 1988). By contrast, in some smooth muscles, opposite pH effects on maximum tension were observed (Spurway and Wray, 1987;Smith et al, 1998).…”

The Effects of pH on the Sodium‐Withdrawal Contractures Evoked from Frog Atrial Trabeculae

“…The steady rise in the tension evoked by Na-free perfusion of atrial fibres between pHo 4 and 10 and the deletrious effects of pHo> 10 are generally consistent with the data for skinned fibres. A direct comparison of the rise in the strength of the Na-free contractures, in atrial preparations with pHo, and the data given by Robertson and Kerrick [1979] for skinned skeletal fibres, can provide a rough estimate of pH; in the former tissue. This comparison shows that when pHo is 4 0, 50 or 9 0, the pHi should be 5 0, 6-0 and 8-0 atrial fibres one might anticipate a faster and larger change in pHi when pHo is altered.…”

“…These results suggest it is a change in pHi that is important and that the apparent absence of an effect between pHo 6 and 7 is due to the activity of buffers in the cytoplasm, especially with the relatively brief changes in pHo used in the present work. Skinned skeletal and cardiac muscle fibres show a steep increase in the maximum tension developed between pH5 0 and 8 5 beyond which there is an irreversible decline [Fabiato and Fabiato, 1978;Robertson and Kerrick, 1979]. The pCa for half maximal activation of tension is decreased by approximately 1 pCa unit for each unit of pH increase, in both types of skinned fibre.…”

“…1970; Brand, Chen and Lehniniger, 1976; Donaildson and Herlrmansen, 1 976: Fa(ibiato and Fabiato, 1978;Robertson and Kerrick, 1979]. A more direct effect of pHo has been found for the membralne CLirrents associated with the cardiac baction potential [Wada a.Ind Goto.…”

The Influences of L(+)-Lactate and pH on Contractile Performance in Rabbit Glycerinated Skeletal Muscle

“…Actually, an obvious decline in intracellular pH is known to take place during intense muscular work [16], and the intramuscular pH changes from a value of approximately 7 at rest to a value approaching 6 during severe fatigue [3,[16][17][18]. The H ϩ produced in muscle cells can directly affect cross-bridge function and lead to the decline in Ca 2ϩ sensitivity [19][20][21], isometric tension [19,[22][23][24], and shortening velocity [23,24].However, it remains unsettled whether lactate anion Japanese Journal of Physiology, 53, 401-409, 2003 Key words: fatigue, skeletal muscle, lactate, acidosis. …”