Ϫ current (ICl,swell) is complex, and multiple signaling cascades are implicated. To determine whether protein tyrosine kinase (PTK) modulates ICl,swell and to identify the PTK involved, we studied the effects of a broad-spectrum PTK inhibitor (genistein), selective inhibitors of Src (PP2, a pyrazolopyrimidine) and epidermal growth factor receptor (EGFR) kinase (PD-153035), and a protein tyrosine phosphatase (PTP) inhibitor (orthovanadate). I Cl,swell evoked by hyposmotic swelling was increased 181 Ϯ 17% by 100 M genistein, and the genistein-induced current was blocked by the selective ICl,swell blocker tamoxifen (10 M). Block of Src with PP2 (10 M) stimulated tamoxifen-sensitive ICl,swell by 234 Ϯ 27%, mimicking genistein, whereas the inactive analog of PP2, PP3 (10 M), had no effect. Moreover, block of PTP by orthovanadate (1 mM) inhibited ICl,swell and prevented its stimulation by PP2. In contrast with block of Src, block of EGFR kinase with PD-153035 (20 nM) inhibited ICl,swell. Several lines of evidence argue that the PP2-stimulated current was ICl,swell: 1) the stimulation was volume dependent, 2) the current was blocked by tamoxifen, 3) the current outwardly rectified with both symmetrical and physiological Cl Ϫ gradients, and 4) the current reversed near the Cl Ϫ equilibrium potential. To rule out contributions of other currents, Cd 2ϩ (0.2 mM) and Ba 2ϩ(1 mM) were added to the bath. Surprisingly, Cd 2ϩ suppressed the decay of ICl,swell, and Cd 2ϩ plus Ba 2ϩ eliminated time-dependent currents between Ϫ100 and ϩ100 mV. Nevertheless, these divalent ions did not eliminate ICl,swell or prevent its stimulation by PP2. The results indicate that tyrosine phosphorylation controls ICl,swell, and regulation of ICl,swell by the Src and EGFR kinase families of PTK is antagonistic.volume-sensitive Cl Ϫ current; AG 1879; PD-153035; orthovanadate; tamoxifen; genistein; epidermal growth factor receptor OSMOTIC SWELLING OR HYDROSTATIC inflation of cardiac myocytes and numerous other tissues evokes the volume-sensitive Cl Ϫ current I Cl,swell . This current is outwardly rectifying, partially inactivated at positive voltages, and blocked by tamoxifen. These biophysical and pharmacological characteristics distinguish I Cl,swell from other Cl Ϫ currents (for reviews, see Refs. 4 and 28). Under isosmotic conditions, I Cl,swell contributes to the background Cl Ϫ current (17, 18) and is activated in models of cardiac disease (12) and by stretching  1 -integrins (7, 8).Functionally, the activation of I Cl,swell influences both cardiac electrical activity (16,30,49) and cell volume (11,12).The signaling that underlies the activation of I Cl,swell is complex, and evidence implicates protein kinases C and A and protein tyrosine kinase (PTK) in its regulation in the heart (4, 28) and other tissues (32). PTK is activated by osmotic swelling of myocytes within 5 s (37, 38) and therefore is well positioned to be an early step in the signaling process. Although substantial evidence indicates that phosphorylation and dephosphorylation o...
