title: Increase in T-type calcium current in atrial myocytes from adult rats with growth hormone-secreting tumors.
abstract: Growth hormone (GH) has pronounced effects on protein synthesis and cell growth in cardiac muscle from adult animals, although the mechanism of its action is not understood. Because Ca2+ has been implicated as a regulator of mitogenic processes in a number of tissues, we investigated whether GH affects the transmembrane movement of Ca2+ through voltage-activated channels of cardiac myocytes. Atrial and ventricular myocytes were isolated from adult rats with GH-secreting tumors and studied electrophysiologically by using patch-clamp techniques. Tumor-bearing rats re-enter an active growth phase and double their body weight over age-matched controls 8 weeks after introduction of the tumor. Atrial myocytes from tumor-bearing animals showed a 3-fold increase in the density of T-type Ca2+ current compared with cells from control animals, although the voltage dependency of activation and inactivation of T-type current was not altered. The increase in T-current density of atrial myocytes preceded by at least a week any measurable change in heart weight, body weight, or myocyte size. L-type Ca2+ currents in atrial and ventricular cells were not affected. The results suggest that a tumor-derived growth factor, most likely GH, can cause a specific enhancement of T-type Ca2+ current in atrial myocytes.
authors.affiliation: Department of Physiology and Biophysics, University of Illinois, Urbana 61801.
authors.forename: X P
authors.initials: XP
authors.lastname: Xu
authors.forename: P M
authors.initials: PM
authors.lastname: Best
mesh_terms: D000818:Animals; D016275:Atrial Function; D001835:Body Weight; D015220:Calcium Channels / Q000502:physiology*; D002460:Cell Line; D005260:Female; D013006:Growth Hormone / Q000378:metabolism*; D006321:Heart / Q000502:physiology / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009929:Organ Size; D010911:Pituitary Neoplasms / Q000378:metabolism / Q000503:physiopathology*; D051381:Rats; D011920:Rats, Inbred WF; D012016:Reference Values
chemical_list: D015220:Calcium Channels; D013006:Growth Hormone