Involvement of different Ca2+ pools during the canine bronchial sustained contraction in Ca2+-free medium: lack of effect of PKC inhibition

• Published in: Naunyn-Schmiedeberg's archives of pharmacology Vol. 358; no. 5; pp. 567 - 573
• Main Authors: Bazán-Perkins, B, Carbajal, V, Sommer, B, Macías-Silva, M, Gonzalez-Martinez, M, Valenzuela, F, Daniel, E E, Montaño, L M
• Format: Journal Article
• Language: English
• Published: Germany 01.11.1998
• Subjects: Animals; Bronchi - drug effects; Bronchi - metabolism; Bronchi - physiology; Bronchoconstriction - drug effects; Calcium - metabolism; Calcium - pharmacology; Carbachol - pharmacology; Cardiotonic Agents - pharmacology; Dogs; Enzyme Inhibitors - pharmacology; Female; Histamine - pharmacology; In Vitro Techniques; Inositol Phosphates - metabolism; Male; Muscle Contraction - drug effects; Muscle, Smooth - drug effects; Muscle, Smooth - metabolism; Muscle, Smooth - physiology; Naphthalenes - pharmacology; Protein Kinase C - antagonists & inhibitors
• ISSN: 0028-1298
• DOI: 10.1007/PL00005294

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.