Role of protein kinase C in calcium sensitization during muscarinic stimulation in airway smooth muscle

Abstract

Muscarinic receptor stimulation increases Ca2+ sensitivity, i.e., the amount of force produced at a constant submaximal cytosolic Ca2+ concentration ([Ca2+]i), in permeabilized smooth muscle preparations. It is controversial whether this increase in Ca2+sensitivity is in part mediated by protein kinase C (PKC). With the use of a β-escin permeabilized canine tracheal smooth muscle (CTSM) preparation, the effect of four putative PKC inhibitors {calphostin C, chelerythrine chloride, a pseudosubstrate inhibitor for PKC [PKC peptide-(19—31)], and staurosporine} on Ca2+sensitization induced by acetylcholine (ACh) plus GTP was determined. Preincubation with each of the inhibitors did not affect subsequent Ca2+ sensitization induced by muscarinic receptor stimulation in the presence of a constant submaximal [Ca2+]i, neither did any of these compounds reverse the increase in Ca2+ sensitivity induced by ACh plus GTP. Administration of a 1,2-diacylglycerol analog, 1-oleoyl-2-acetyl- sn-glycerol, did not induce Ca2+ sensitization at a constant submaximal [Ca2+]i. Thus we found no evidence that PKC mediates increases in Ca2+ sensitivity produced by muscarinic receptor stimulation in permeabilized CTSM.

8-Bromo-cAMP decreases the Ca2+sensitivity of airway smooth muscle contraction through a mechanism distinct from inhibition of Rho-kinase

“…Although CCh-induced Ca 2ϩ sensitization was inhibited by both 8-BrcAMP and Y-27632 to a similar extent, GTP␥S-induced Ca 2ϩ sensitization was resistant to 8-BrcAMP. In permeabilized canine tracheal smooth muscle, both PDBu and acetylcholine induce Ca 2ϩ sensitization (3,4). Rho/Rho-kinase-mediated signaling may be distinct from the PKC system because the effects of saturating concentrations of GTP␥S and PDBu were additive (9).…”

“…Hepler et al (8) showed that purified G q had only a slight binding affinity to GTP␥S. Additionally, AlF 4 Ϫ is known to activate the trimetric G protein. Contraction induced by AlF 4 Ϫ but not that induced by GTP␥S was insensitive to GDP␤S (15,28).…”

“…Additionally, AlF 4 Ϫ is known to activate the trimetric G protein. Contraction induced by AlF 4 Ϫ but not that induced by GTP␥S was insensitive to GDP␤S (15,28). These findings suggest that GTP␥S mainly activates small G proteins, although the precise mechanism is still unknown.…”

Upregulation of rhoA mRNA in Bronchial Smooth Muscle of Antigen-induced Airway Hyperresponsive Rats.

“…Recently, additional mechanisms have been suggested in agonist-induced smooth muscle contraction as a result of studies which used the simultaneous measurement of force development and intracellular Ca 2+ concentration, as well as those on various smooth muscle preparations which have been chemically permeabilized. It has been demonstrated that agonist stimulation increases myofilament Ca 2+ sensitivity in β-escin-permeabilized smooth muscle of the rat coronary artery (Satoh et al, 1994), guinea pig vas deferens (Fujita et al, 1995), canine trachea (Bremerich et al, 1997) and rat bronchus (Chiba et al, 1999b). Although the detailed mechanism is not fully understood, many investigators have suggested the participation of RhoA, a monomeric GTP binding protein, in the agonist-induced Ca 2+ sensitization (e.g., Fujita et al, 1995;Gong et al, 1997;Chiba et al, 1999b).…”

Mechanism of Inhibitory Effect of Prednisolone on RhoA Upregulation in Human Bronchial Smooth Muscle Cells

“…Recently, additional mechanism, termed Ca 2ϩ sensitization, has also been suggested to be involved in the agonist-induced smooth muscle contraction. It has been demonstrated that agonist stimulation increases myofilament Ca 2ϩ sensitivity in permeabilized smooth muscles of the rat coronary artery, 2) guinea pig vas deferens, 3) canine trachea, 4) and rat bronchus. 5) Although the detailed mechanism is not fully cleared, an involvement of RhoA, a monomeric GTP-binding protein, in agonist-induced Ca 2ϩ sensitization has been suggested by many investigators.…”