Calcium exchange and contraction strength of guinea pig atrium in normal and hypertonic media.
A Krebs-Henseleit (KH) medium made hypertonic by adding nonpermeant molecules substantially increased the isometric peak tension at steady-state contractions below 3 per sec in guinea pig atrium at 27 degrees C. Action potential durations were decreased. KH plus 100 mM raffinose or sucrose resulted in similar and nearly maximal changes which were essentially reversible upon return to normal KH. When one active contracting atrium was used to passively stretch a second atrium, the difference in Ca ion exchange (1 min exchange with the extracellular space) between active and stretched atria significantly increased at 1 per sec and at 2 per sec in going from normal to 100 mM hypertonic KH. The calculated mean Ca ion cellular exchange per beat per 100 g of cells (a) doubled in changing from normal to 100 mM hypertonic KH, and (b) decreased slightly in changing from contractions of 1 per sec to 2 per sec in normal KH. These data are consistent with the hypothesis (a) that Ca ion entry per beat from the extracellular space is proportional to membrane depolarized time with a constant medium and a steady-state condition, and the hypothesis (b) that 100 mM hypertonicity doubles the Ca ion entry rate during depolarization. These data enable rejection of the hypothesis that the peak tension is proportional to the Ca ion entry per beat from the extracellular space under steady-state conditions, and suggest that any additional Ca ion involved in the larger contractions at higher frequencies comes from an increase in Ca ion available from intracellular stores.
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002127:Calcium Isotopes; D005110:Extracellular Space; D006168:Guinea Pigs; D006325:Heart Atria / Q000378:metabolism; D006982:Hypertonic Solutions; D008353:Mannitol / Q000378:metabolism; D009119:Muscle Contraction; D009206:Myocardium / Q000378:metabolism*; D009994:Osmolar Concentration; D013395:Sucrose / Q000378:metabolism
D002127:Calcium Isotopes; D006982:Hypertonic Solutions; D008353:Mannitol; D013395:Sucrose; D002118:Calcium
J Gen Physiol. 1963 Mar;46:679-702
13999359
Am J Physiol. 1963 Jun;204:957-62
14034035
J Pharmacol Exp Ther. 1964 Jan;143:120-30
14118077
Proc R Soc Lond B Biol Sci. 1964 Oct 27;160:489-501
14214778
J Gen Physiol. 1965 Jan;48:455-79
14284779
Am J Physiol. 1964 Feb;206:270-82
14120426
Circ Res. 1965 Jul;17:78-89
14302554