Streptomycin reverses a large stretch induced increases in [Ca2+]i in isolated guinea pig ventricular myocytes.
OBJECTIVE
The aim was to test the hypothesis that in single guinea pig ventricular myocytes a large stretch induced increase in resting calcium was sensitive to the mechanosensitive channel blocker streptomycin.


METHODS
Carbon fibres were used to stretch cells loaded with the fluorescent calcium indicator indo-1. Force, sarcomere length, and internal calcium activity ([Ca2+]i) were measured.


RESULTS
In approximately 60% of the cells studied, a stretch which increased sarcomere length by approximately 6% caused a large increase in [Ca2+]i (up to 60% of the size of a [Ca2+]i transient at 0.25 Hz). When a mixture of antibiotics (streptomycin-penicillin) was used in solutions to isolate and store cells, this phenomenon was never observed (n = 19 cells). Direct application of physiological saline solution (PSS) could not reverse the increase in [Ca2+]i within 60 s of application (n = 7 cells). Direct application of penicillin [1000 IU per 50 ml (40 microM)] reversed the increase in [Ca2+]i within 60 s of application in only 3/7 cells. In contrast direct application of the aminoglycoside antibiotic streptomycin (40 microM) rapidly reversed the large increase in [Ca2+]i induced by stretch in each of 13 cells [within 18(SD 10) s of application]. Acute application of 40 microM streptomycin did not modify L-type Ca2+ currents measured under whole cell patch clamp conditions. Measurement of the resting tension--sarcomere length curves in cells stored in solution containing streptomycin and penicillin revealed two populations of cells on the basis of their stiffness.


CONCLUSIONS
This stretch induced increase in [Ca2+]i may be associated with stretch activated arrhythmias in the heart. The effects of streptomycin are consistent with its reported inhibitory action on stretch activated channels.
Gannier
F
F
Laboratoire de Physiologie des Cellules Cardiaques et Vasculaires, CNRS EP 21, Faculté des Sciences, Tours, France.
White
E
E
Lacampagne
A
A
Garnier
D
D
Le Guennec
J Y
JY
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D048429:Cell Size / Q000187:drug effects; D006168:Guinea Pigs; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010406:Penicillins / Q000494:pharmacology; D012518:Sarcomeres / Q000648:ultrastructure; D013307:Streptomycin / Q000494:pharmacology*
D010406:Penicillins; D002118:Calcium; D013307:Streptomycin