Swelling and Swelling-activated Currents in Feline Ventricular MyocytesNorthwestern University, Department of Pharmacology, 1997 Feline ventricular myocytes swell when exposed to hypotonic solutions. Swelling is associated with the appearance of an outwardly-rectifying transmembrane ionic current. The whole-cell patch-clamp conformation, video-microscopy and hypotonic (180 mOsm) solutions were used to investigate the nature of this current and its relationship to myocyte swelling. The swelling-activated current (I$\sb{\rm swell}$) was found to consist of a cation and an anion component. The cation component (I$\sb{\rm cat-swell}$), isolated by using chloride-free solutions, was insensitive to block by barium (0.5 mM), cesium (10 mM) and gadolinium (50 $\mu$M) ions, but was blocked by tetraethylammonium acetate (10 mM) applied to the inner surface of the membrane. The anion component, recorded in potassium-free solutions, was chloride-sensitive and was designated I$\sb{\rm Cl-swell}$. It was present in 50% of patched myocytes and was activated by osmotic swelling as well as by application of positive pressure to the patch pipette. When I$\sb{\rm Cl-swell}$ was present the plot of current amplitude against myocyte cross-sectional area was linear, i.e. the magnitude of I$\sb{\rm Cl-swell}$ increased with increasing swelling and declined during shrinking. This linear relationship was rendered non-linear by cytochalasin D (15 $\mu$g/ml) which disrupts F-actin filaments, but not by colchicine (2.5 $\mu$M) which disrupts microtubules. As I$\sb{\rm Cl-swell}$ appeared grossly similar to the cAMP-dependent chloride current (I$\sb{\rm Cl-cAMP}$), myocytes were tested for responses to swelling as well as cAMP-elevating agents such as isoproterenol (1 $\mu$M) and forskolin (10 $\mu$M). Four populations of myocytes were identified: those that developed a chloride current both on swelling and cAMP elevation, those responding to only one or the other, and those responding to neither. The current activated by swelling, but not forskolin, was blocked by DIDS (100 $\mu$M) and could be activated in absence of pipette ATP and in the presence of AMP-PNP (200 $\mu$M). Based on these findings it was concluded that I$\sb{\rm Cl-swell}$ and I$\sb{\rm Cl-cAMP}$ are different currents carried by different types of chloride channels. Swelling-activated currents depolarize the myocyte resting membrane potential and shorten its action potential duration. Therefore, they may contribute to cardiac arrhythmias observed in conditions associated with cardiomyocyte swelling such as ischemia, infarction and reperfusion. |
Common terms and phrases
actin cytoskeleton actin filaments action potential activation of Icl-swell anion application arrhythmias atrial myocytes blocked Ca2+ capacitance cardiac myocytes cat ventricular myocytes cell CFTR changes in myocyte channel activation Chapter chloride channels component of Iswell current in feline current-area plot currents recorded cytochalasin cytoskeleton depolarizing described effect of forskolin experiments feline ventricle feline ventricular myocytes Figure forskolin Gadolinium genistein heart hypertonic hypotonic solution Icat-swell Icl-swell and ICI-CAMP increase inhibited internal solution internal TEA intracellular ion channels isoproterenol Isotonic Hypotonic isotonic solution kinase inhibitor mean data measurements mechanosensitive channels mechanotransduction mOsm myocyte area myocyte dimensions myocyte swelling normal osmotic swelling outward current outwardly rectifying pA/pF panel patch pipette permeability phosphorylation physiological pipette present response to swelling reversal potential shows ẞ-agonists stretch-activated cation channels suction swelling in hypotonic swelling-activated cation swelling-activated channels swelling-activated chloride current swelling-activated current voltage clamp voltage clamp protocol volume-clamp whole-cell current