ISSN:
1432-2013
Keywords:
Calcium current
;
Phosphatase
;
Kinase
;
Development
;
Microcystin
;
Okadaic acid
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract We used whole-cell voltage clamp to compare the modulation of calcium current density (I Ca, picoampere per picofarad) of freshly isolated, adult and newborn rabbit heart in response to intracellular application of microcystin and okadaic acid, both of which block phosphatase activity of phosphatase types 1 and 2A. Newborn cells showed a much larger response to the intracellular application of either microcystin or okadaic acid than did adult cells. In newborn cells, the application of microcystin produced an increase in I Ca which appeared to maximize I Ca, as shown by the rise in I Ca to levels which could be reached by application of 10 μM forskolin or by the intracellular application of 200 μM 3′,5′-cyclic adenosine monophosphate (cAMP). In adult cells, the maximal response to microcystin was considerably less than that obtainable with forskolin or cAMP. After achieving a maximal response with microcystin, the addition of forskolin increased I Ca further in adult cells but elicited no additional response in newborn cells. The treatment of cells with 0.1 μM isoproterenol, a concentration approximately equal to that required for a half-maximal response, strongly potentiated the effect of microcystin in newborn cells, but not in adult cells. We propose that newborn rabbit heart cells compared with adult rabbit heart cells have a greater level of protein phosphatase activity (perhaps combined with a somewhat greater kinase activity), a greater proportion of the protein phosphatase activity in the form of protein phosphatase type 1 (which is inhibited by isoproterenol) and a greater dependence on the inhibition of protein phosphatase as a mechanism of action of isoproterenol, compared with the increase in kinase activity on calcium channels.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00374252
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