Involvement of different Ca2+ pools during the canine bronchial sustained contraction in Ca2+-free medium: lack of effect of PKC inhibition.
We evaluated the role of protein kinase C (PKC) in the sustained bronchial contraction (SBC) induced by carbachol (Cch) or histamine in a Ca2+-free medium and the possibility that each agonist uses a different Ca2+ store for this response. We studied third-order bronchi and airway smooth muscle (ASM) from first-order bronchi dissected free of cartilage and epithelium. Bronchial and ASM responsiveness to Cch or histamine were evaluated in Krebs solution (2.5 mM Ca2+) and in Ca2+-free medium. Cch and histamine induced an SBC in bronchial tissues in Ca2+-free medium. In ASM each agonist produced a transient contraction, but the response to histamine was much smaller. Cch induced a concentration-dependent accumulation of inositol phosphates (IPs) in both bronchi and ASM; however, histamine did not induce significant accumulation of IPs. Repeated exposure to histamine in bronchial rings abolished contractile responses in Ca2+-free media, but Cch added afterwards still produced a sustained contraction. This response was blocked when bronchial tissues were preincubated with 10 microM cyclopiazonic acid (CPA). Brief incubation of these preparations with a high EGTA concentration (1 mM) abolished the histamine-induced SBC. The SBC induced by Cch or histamine in Ca2+-free medium was not affected by the preincubation of the tissues with calphostin C, chelerythrine or staurosporine. We concluded that Cch mobilizes Ca2+ from two different sources during the SBC in Ca2+-free medium: from a CPA-sensitive one from sarcoplasmic reticulum (SR) and from a putative extracellular membrane Ca2+ pool sensitive to 1 mM EGTA, and neither process involved PKC activation. Histamine appeared to utilize the extracellular membrane pool only.
Bazán-Perkins
B
B
Departamento de Farmacología, Facultad de Medicina, UNAM, México DF, México.
Carbajal
V
V
Sommer
B
B
Macías-Silva
M
M
Gonzalez-Martinez
M
M
Valenzuela
F
F
Daniel
E E
EE
Montaño
L M
LM
D000818:Animals; D001980:Bronchi / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D016084:Bronchoconstriction / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002217:Carbachol / Q000494:pharmacology; D002316:Cardiotonic Agents / Q000494:pharmacology; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D009281:Naphthalenes / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors
D002316:Cardiotonic Agents; D004791:Enzyme Inhibitors; D007295:Inositol Phosphates; D009281:Naphthalenes; D006632:Histamine; D002217:Carbachol; D011493:Protein Kinase C; C058819:calphostin C; D002118:Calcium