CAMP-dependent channels

In parallel, activity of adenylate cyclase is inhibited by Ca2+, and the ion activates the membrane-embedded CAM to close the cAMP-dependent channels. In addition, CAM-PDE is induced to hydrolyze the messenger molecules rapidly. 4) Finally, Ca2+ activates the cytoplasmic CAM to enhance the activity of Ca2+-translocating ATPase, causing the cells to return to the resting state. 

Becq, F., M. D. Merten, M. A. Voelckel, M. Gola, and C. Figarella. 1993. Characterization of cAMP dependent CFTR-chloride channels in human tracheal gland cells. FEBS Lett 321 73-8. 

TTie second messenger, for example cyclic adenosine monophosphate (cAMP), then activates cAMP-dependent protein kinase which modulates the function of a broad range of membrane receptors, intracellular enzymes, ion channels and transcription factors. 

Autonomic receptors further regulate calcium influx through the sarcolemma (Fig. 15.1). (3-Adrenergic stimulation results in the association of a catalytic subunit of a G protein coupled to the (3-receptor. This stimulates the enzyme adenylyl cyclase to convert ATP to cyclic adenosine monophosphate (cAMP). Increasing cAMP production results in a cAMP-dependent phosphorylation of the L-type calcium channel and a subsequent increase in the probability of the open state of the channel. This translates to an increase in transsarcolemmal calcium influx during phase 2 (the plateau phase) of the cardiac muscle action potential. The effects of transient increases in intracellular levels of cAMP are tightly con-... 

Gap junction conductance (gj) of neonatal rat heart cells varies with temperature (37 °C, 48.3 nS 14 °C, 21.4 nS -2°C, 17.5 nS) [Bukauskas and Weingart, 1993] so that gj has been assumed to be at least in part enzymatically controlled. Several protein kinases are known to be involved in the regulation of the gap junction channels. However, the situation is rather complicated since the same protein kinase may enhance or reduce gap junctional conductance in different tissues or in different species. Thus, generalizations should be avoided and the specific condition has to be taken into account. One of the first to be described was protein kinase A (PKA), the cAMP-dependent protein kinase, which can enhance junctional conductance in hepatocytes coupled via Cx32 and Cx26 [Saez et al., 1986, 1990]. Similarly, an increase in junctional conduc-... 

Fitzgerald, E. M., Okuse, K., Wood, J. N., Dolphin, A. C., Moss, S. J. cAMP-dependent phosphorylation of the tetrodotoxin-resistant voltage-dependent sodium channel SNS, J. Physiol. 1999, 516, 433-446. 

A functional map of the Na+ channel a subunits. The transmembrane folding model of the a subunit is depicted with experimentally demonstrated sites of cAMP-dependent phosphorylation (P), interaction of site-directed antibodies that define transmembrane orientation covalent attachment... 

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