Modulation of calcium channel expression in cardiac myocytes of rats during growth hormone-induced growth or normal postnatal development
Xu, Xiao Ping
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Permalink
https://hdl.handle.net/2142/23416
Description
Title
Modulation of calcium channel expression in cardiac myocytes of rats during growth hormone-induced growth or normal postnatal development
Author(s)
Xu, Xiao Ping
Issue Date
1992
Doctoral Committee Chair(s)
Best, Philip M.
Department of Study
Physiology
Discipline
Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Language
eng
Abstract
Voltage-dependent Ca$\sp{2+}$ currents of cardiac myocytes were studied using patch-clamp techniques. T-type Ca$\sp{2+}$ current density of atrial myocytes was found to be positively correlated with the plasma growth hormone levels and the growth rate of atrial myocytes in normally developing Sprague-Dawley rats, adult Wistar-Furth rats made to reenter an active growth phase following implantation of a growth hormone-secreting tumor, and mutant dwarf rats with retarded growth due to a specific deficiency in pituitary growth hormone synthesis. The voltage and time dependent activation and inactivation of T-type Ca$\sp{2+}$ current are not changed in spite of the changes in T-current density. The unchanged macroscopic current properties and constant single T-channel current suggest that the change in T-current density is likely due to a change in membrane density of T-type Ca$\sp{2+}$ channels rather than a change in the channel protein itself. Though atrial T-current density increases when plasma growth hormone levels are high, it is difficult to prove the involvement of growth hormone in regulating Ca$\sp{2+}$ channel expression because of the complication from other hormones and growth factors. It is also possible that the correlation between atrial T-current density and plasma growth hormone levels is merely accidental. The up-regulation of T-type Ca$\sp{2+}$ channel density during active growth is specific for atrial myocytes, since T-type Ca$\sp{2+}$ current is not induced in ventricular myocytes from the tumor-bearing rats. High T-current density during the period of active growth of atrial myocytes supports the idea that T-type Ca$\sp{2+}$ channels may have some role in embryonic/postnatal development in certain tissues. L-type Ca$\sp{2+}$ channels are regulated in a different way. In contrast to T-type Ca$\sp{2+}$ current, L-type Ca$\sp{2+}$ current density remains constant in both atrial and ventricular cells from rats during either normal postnatal development in young rats or induced active growth in adult rats bearing growth hormone-secreting tumors. The constant L-current density may be important to keep up Ca$\sp{2+}$ influx with increased cell size to support normal cardiac contraction.
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