Modulation of Large Conductance Ca2+-activated K+ Channel of Skin Fibroblast (CRL-1474) by Cyclic Nucleotides

Potassium channels in human skin fibroblast have been studied as a possible site of Alzheimer disease pathogenesis. Fibroblasts in Alzheimer disease show alterations in signal transduction pathway such as changes in Ca2+ homeostasis and/or Ca2+-activated kinases, phosphatidylinositol cascade, protein kinase C activity, cAMP levels and absence of specific K+ channel. However, little is known so far about electrophysiological and pharmacological characteristics of large-conductance Ca2+-activated K+ (BKCa) channel in human fibroblast (CRL-1474). In the present study, we found Iberiotoxin- and TEA-sensitive outward rectifying oscillatory current with whole-cell recordings. Single channel analysis showed large conductance K+ channels (106 pS of chord conductance at +40 mV in physiological K+ gradient). The 106 pS channels were activated by membrane potential and [Ca2+]i, consistent with the known properties of BKCa channels. BKCa channels in CRL-1474 were positively regulated by adenylate cyclase activator (10microM forskolin), 8-Br-cyclic AMP (300microM) or 8-Br-cyclic GMP (300microM). These results suggest that human skin fibroblasts (CR-1474) have typical BKCa channel and this channel could be modulated by c-AMP and c-GMP. The electrophysiological characteristics of fibroblasts might be used as the diagnostic clues for Alzheimer disease.

The Effects of Chronic Carbamazepine Administration on Protein Kinase A and Protein Kinase C Activities in Rat Brain

OBJECTIVE: Many evidences suggest that patients with bipolar disorder have functional abnormalities in their postreceptor signal transduction pathways, and mood stabilizing effect of lithium is exerted by modulating this dysfunctioning system. Carbamazepine, an antiepileptic agent, is also known to be effective in the treatment and prevention of bipolar disorder. But the precise mechanism of action of the drug is still poorly understood. This study was performed to elucidate the possible therapeutic mechanism of carbamazepine. METHOD: The effects of chronic carbamazepine administration on protein kinase A and protein kinase C activities in frontal cortex of rat brain after 2 weeks of drug administration were measured and compared with those of control subjects. RESULTS: Mean(+/-SE) value of activity(phosphate transfer micromol/mg of protein, min) or protein kinase A in control and test group was 0.249563+/-0.036 and 0.539853+/-0.078, and that of protein kinase C was 0.654817+/-0.053 and 1.146205+/-0.052 respectively, being increased in test group. And differences between the two groups were statistically significant for both enzymes(protein kinase A ; p<0.01, protein kinase C ;p<0.001). CONCLUSION: These results show that chronic carbamazepine administration increases protein kinase A and C activities, and concerning the possible mode of therapeutic action in bipolar disorder it is suggested that enhanced enzymes phosphorylate receptor-G-protein-effector complexes to dampen hyperfunctioning neuronal activity and thus stabilize the system.