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Studies of radiocalcium efflux in single barnacle muscle fibres: effects of procaine and external divalent cations
Author(s) -
Chen Stephen S.
Publication year - 1974
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1974.sp010526
Subject(s) - procaine , efflux , chemistry , egta , biophysics , divalent , stimulation , microinjection , calcium , washout , biochemistry , pharmacology , endocrinology , medicine , biology , organic chemistry
1. 45 Ca efflux from single barnacle muscle fibres loaded with radio‐calcium by microinjection was studied. 2. The 45 Ca washout curve consisted of three exponential phases with half‐times of 4·8, 12·6 and 111·1 min. 3. Removal of external Ca 2+ reduced 45 Ca efflux by 65%. The 45 Ca efflux recovered upon restoring external Ca 2+ , the magnitude of the recovery being dependent upon the external Ca 2+ concentration. 10 m M procaine was found to reduce the magnitude of the recovery. 4. Removal of external Mg 2+ resulted in a 38% increase in 45 Ca efflux. 5. External application of procaine at pH 7·8 caused a dose‐dependent inhibition of 45 Ca efflux. The magnitude of the inhibition was reduced in the presence of low external Ca 2+ concentrations. 10 m M procaine at pH 9·3 caused a biphasic effect: inhibition was followed by stimulation. 6. Microinjection of 0·5 M procaine caused only inhibition of 45 Ca efflux, whereas microinjection of 1·5 M procaine caused stimulation followed by inhibition. These effects were observed at an external pH of 7·8 and 9·3. 7. Injection of 100 m M ‐EGTA abolished the stimulatory but not the inhibitory effect produced by procaine injection. 8. These results are interpreted as indicating that a major fraction of the 45 Ca efflux involves Ca‐Ca exchange which is inhibited by the charged form of procaine in a non‐competitive manner at the external surface of the muscle fibre. The stimulatory action is attributed to release by procaine of Ca 2+ from internal binding sites.