K⁺ currents regulate the resting membrane potential, proliferation, and contractile responses in ventricular fibroblasts and myofibroblasts

Abstract

Despite the important roles played by ventricular fibroblasts and myofibroblasts in the formation and maintenance of the extracellular matrix, neither the ionic basis for membrane potential nor the effect of modulating membrane potential on function has been analyzed in detail. In this study, whole cell patch-clamp experiments were done using ventricular fibroblasts and myofibroblasts. Time- and voltage-dependent outward K(+) currents were recorded at depolarized potentials, and an inwardly rectifying K(+) (Kir) current was recorded near the resting membrane potential (RMP) and at more hyperpolarized potentials. The apparent reversal potential of Kir currents shifted to more positive potentials as the external K(+) concentration ([K(+)](o)) was raised, and this Kir current was blocked by 100-300 muM Ba(2+). RT-PCR measurements showed that mRNA for Kir2.1 was expressed. Accordingly, we conclude that Kir current is a primary determinant of RMP in both fibroblasts and myofibroblasts. Changes in [K(+)](o) influenced fibroblast membrane potential as well as proliferation and contractile functions. Recordings made with a voltage-sensitive dye, DiBAC(3)(4), showed that 1.5 mM [K(+)](o) resulted in a hyperpolarization, whereas 20 mM [K(+)](o) produced a depolarization. Low [K(+)](o) (1.5 mM) enhanced myofibroblast number relative to control (5.4 mM [K(+)](o)). In contrast, 20 mM [K(+)](o) resulted in a significant reduction in myofibroblast number. In separate assays, 20 mM [K(+)](o) significantly enhanced contraction of collagen I gels seeded with myofibroblasts compared with control mechanical activity in 5.4 mM [K(+)](o). In combination, these results show that ventricular fibroblasts and myofibroblasts express a variety of K(+) channel alpha-subunits and demonstrate that Kir current can modulate RMP and alter essential physiological functions.

Neonatal rat cardiac fibroblasts express three types of voltage-gated K+ channels: regulation of a transient outward current by protein kinase C

“…The cell membrane capacity of the fibroblasts ranged from 22 to 82 pF, with a mean Ϯ SE value of 48 Ϯ 2 pF (n ϭ 60 cells). Consistent with previous studies (4,27), no voltage-dependent inward Ca 2ϩ currents were measured in the cardiac fibroblasts. In addition, voltage steps applied from the holding potential of Ϫ80 mV to potentials ranging from Ϫ120 through Ϫ90 mV failed to elicit Ba 2ϩ -sensitive inward-rectifier currents (Fig.…”

“…The presence of Kv1.4 subunits in the fibroblast cell lyates suggests that this protein, and not the Kv4.2 subunit, is responsible for the fibroblast I to . Because I to were not previously identified in adult cardiac fibroblasts or myofibroblasts (4,23), our results indicate that developmental factors may be important in determining the electrical properties of the cardiac fibroblasts.…”

“…The ion channel responsible for this current was not identified, nor was the ionic basis for the resting potential of the neonatal fibroblasts (Ϫ20 to Ϫ40 mV) determined in the study. Recently, Giles and colleagues (4,23) analyzed ion channels in freshly dissociated adult cardiac fibroblasts and cultured myofibroblasts. Two types of K ϩ currents were measured in the fibroblasts: a voltage-dependent delayed-rectifier current (I K ) (4,23) and an inward-rectifying current (4).…”

“…Recently, Giles and colleagues (4,23) analyzed ion channels in freshly dissociated adult cardiac fibroblasts and cultured myofibroblasts. Two types of K ϩ currents were measured in the fibroblasts: a voltage-dependent delayed-rectifier current (I K ) (4,23) and an inward-rectifying current (4). This latter current contributes to the relatively negative resting membrane potential (Ϫ50 mV) recorded in the adult fibroblasts.…”

The Role of Casein Kinase 2 in Ion Channel Remodeling After Myocardial Infarction

“…Cardiac inward rectifying potassium currents (Ik1) play an important role in shaping action potentials, which is a key character representing the electrical activity made by a multitude of various ion channels and transporters [3]. The cardiac IK1 stabilizes the resting membrane potential and is responsible for shaping the initial depolarization and final repolarization of the action potential [4,5]. Indeed, infarction generally entails significant cellular and molecular remodeling in the left ventricle, resulting in functional and biochemical alterations of the myocardium due to the modulation of IK1 [2].…”