Actions of the anti-oestrogen agent clomiphene on outward K+ currents in rat ventricular myocytes

Abstract

1. The effects of clomiphene (CLM) on cardiac outward K+ current components from rat isolated ventricular myocytes were investigated using the whole-cell patch-clamp technique. Clomiphene (10 micromol/L) significantly inhibited both peak (Ipeak) and end-pulse (Ilate) outward currents (elicited by a 500 msec voltage step from -40 to +50 mV in the presence of K+-containing intracellular and extracellular solutions) by approximately 37% (n = 6; P < 0.01) and 49% (n = 6; P < 0.01), respectively. In contrast, CLM had no effect on outward currents when K+-free solutions were used. 2. A double-pulse protocol and Boltzmann fitting were used to separate individual K+ current components on the basis of their voltage-dependent inactivation properties. At potentials positive to -80 mV, two inactivating transient outward components (Ito) and (IKx) and a non-inactivating steady state component (Iss) could be distinguished. 3. Clomiphene inhibited both Ito and Iss. The maximal block of Ito and Iss induced by CLM (100 micromol/L) was approximately 61% (n = 5) and 43% (n = 5) with IC50 values of 1.54 +/- 0.39 and 2.2 +/- 0.4 micromol/L, respectively. In contrast, the peak magnitude of IKx was unaltered by CLM, although its time-course of inactivation was accelerated. 4. Further experiments whereby myocytes were superfused with the vasoactive peptide endothelin (ET)-1 (20 nmol/L) revealed that CLM (10 micro mol/L) completely abolished the ET-1-sensitive component of Iss. 5. Our findings demonstrate, for the first time, the effects of CLM on distinct cardiac K+ current components and show that CLM modulates the voltage-gated K+ current components Ito and IKx and inhibits the steady state outward current Iss in rat ventricular myocytes.

Resolution of hyposmotic stress in isolated mouse ventricular myocytes causes sealing of t‐tubules

“…This hypothesis is strongly supported by our recent study showing that various types of relatively mild stress may lead to significant detubulation characterized, in particular, by the disappearance of electrophysiological markers of intact t-tubules, such as I K1 tail currents (Cheng et al 2011). In further support for this, inspection of published whole-cell recordings of relevant K + currents shows that in several previous studies I K1 tail currents are essentially missing (London et al 1998;Xu et al 1999;Bodi et al 2003;Borg et al 2004;Wang et al 2005), while they can be clearly seen in others (Tomita et al 1994;Wickenden et al 1999;Clark et al 2001;Cheng et al 2011), suggesting significant variability in the integrity of the t-tubular system due to different experimental conditions. The data in our study show that t-tubules are well preserved during the myocyte isolation procedure and various other manipulations (e.g.…”

Effect of clomiphene on [Ca2+]i rises and cell viability in rabbit corneal epithelial cells

“…At the cellular level, clomiphene increased cytosolic free Ca 21 levels ([Ca 21 ] i ) in human prostate cancer cells [Jiann et al, 2002], human osteoblasts [Chen et al, 2001], and bladder cancer cells [Jan et al, 2000] and to inhibit angiogenesis [Manolopoulos et al, 2000]. Electrophysiologically, clomiphene was thought to modulate the activity of outward K 1 currents in rat ventricular myocytes [Borg et al, 2004], and to inhibit volumeregulated anion channels in endothelial cells [Maertens et al, 2001]. Cytotoxic effects have also been reported for clomiphene in different cell types, including lymphoma cells [Low and Hwang, 1995], ovarian follicular cells [Chaube et al, 2005], and leukemic cells [Hayon et al, 1999].…”