Shuba, Lesya.2014-10-2119961996AAINN15973http://hdl.handle.net/10222/55149Protein tyrosine kinase (PTK) inhibitor genistein (GST), inactive analogue daidzein, and phosphotyrosine phosphatase (PTPase) inhibitor Na$\sb3\rm VO\sb4(VO\sb4$) were used to modify tyrosine phosphorylation in guinea pig ventricular myocytes configured for recording of whole-cell Cl$\sp-$ current ($I\sb{\rm Cl}$).Inactive daidzein failed to activate significant $I\sb{\rm Cl}$, and GST-activated $I\sb{\rm Cl}$ was rapidly and reversibly inhibited by 0.1-1 mM VO$\sb4$.$I\sb{\rm Cl}$ activated by GST had biophysical and pharmacological properties similar to those of protein kinase A (PKA)-regulated, cystic fibrosis transmembrane conductance regulator (CFTR) $I\sb{\rm Cl}$ activated by forskolin (FSK). Both FSK-activated $I\sb{\rm Cl}$ and GST-activated $I\sb{\rm Cl}$ were absent in CFTR-lacking rat ventricular myocytes.The concentration of GST required for half-maximal activation ($EC\sb{50}$) of Cl$\sp-$ conductance ($g\sb{\rm Cl}$) by GST was $\sim$93 $\mu$M, and $g\sb{\rm Cl}$ activated by 500 $\mu$M GST (9.4 $\pm$ 1.9 nS) was as large as that (8.3 $\pm$ 1 nS) activated by maximally-effective 5 $\mu$M FSK.Submaximally-effective concentrations of GST and FSK activated $I\sb{\rm Cl}$ in a synergistic manner. GST (50 $\mu$M) incremented $I\sb{\rm Cl}$ pre-activated by 5 $\mu$M FSK or 1 mM cAMP dialysate, but not $I\sb{\rm Cl}$ pre-activated by FSK in myocytes treated with serine/threonin phosphatase (PSPase) inhibitor okadaic acid (OA). However, GST action was enhanced in non-FSK-treated OA-dialysed myocytes.These findings, and others from experiments in which PKA activity prior to GST application was either stimulated or depressed, indicate that the activation of $I\sb{\rm Cl}$ by GST is not mediated via stimulation of the PKA pathway, or via inhibition of PSPase. The GST-induced reduction in tyrosine phosphorylation appears to promote CFTR channel opening by enhancing the phosphorylation of channel PKA-sites, and/or by relieving strong tonic inhibition of channel opening caused by tyrosine phosphorylation on a channel or extra-channel moiety.Thesis (Ph.D.)--Dalhousie University (Canada), 1996.Biology, Animal Physiology.text