Caffeine-induced contracture in oesophageal striated muscle of normotensive and hypertensive rats.
To elucidate whether properties of the sarcoplasmic reticulum are altered, not only in vascular smooth muscle, but also in visceral striated muscle of spontaneously hypertensive rats (SHR), caffeine-induced contractures in oesophageal striated muscle of Wistar Kyoto rats (WKY) and stroke-prone SHR (SHRSP) were compared. In both preparations, 30 mM caffeine induced a contracture with two components. The second component, which was diminished by extracellular Ca(2+) removal or Ni(2+) but not by verapamil, was much smaller in SHRSP. Both components and differences between WKY and SHRSP coincided with changes in intracellular Ca(2+). Although membrane potential was identical between these preparations, caffeine induced slight depolarization only in WKY preparations. Similar depolarization was observed with 10 mM K(+), which induced no contraction. It is suggested that the first and the second components of caffeine-induced contracture were induced by Ca(2+) released from sarcoplasmic reticulum and by Ca(2+) that entered through channels activated by sarcoplasmic reticulum Ca(2+) depletion, respectively. In SHRSP preparations, Ca(2+) from the latter pathway was clearly decreased, although this change is thought not to be related to the initiation of hypertension. These results suggest that Ca(2+) handling properties of cell membrane and sarcoplasmic reticulum are generally altered in muscles of SHRSP.
Sekiguchi
Fumiko
F
Department of Anatomy and Physiology, Faculty of Pharmaceutical Sciences, Kinki University, 3-4-1 Kowakae, Osaka Higashiosaka 577-8502, Japan.
Kawata
Kyoko
K
Komori
Mayumi
M
Sunano
Satoru
S
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D004947:Esophagus / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology; D006973:Hypertension / Q000503:physiopathology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000502:physiology / Q000503:physiopathology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012433:Ryanodine / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D002121:Calcium Channel Blockers; D000697:Central Nervous System Stimulants; D012433:Ryanodine; D002110:Caffeine; D014700:Verapamil; D002118:Calcium