Electrically stimulated contraction accelerates protein synthesis rates in adult feline cardiocytes

Abstract

Cardiocytes were induced to contract via electrical field stimulation with an 8 V/cm electrical square-wave pulse of 5 ms at 0.125-2.0 Hz for up to 6 h. Protein synthesis rates were measured as rate of incorporation of [3H]-phenylalanine into total cell protein. Rates of protein synthesis were accelerated 43 +/- 4%, P < 0.001, by 4 h. The acceleration of total protein synthesis showed a frequency dependence between 0.125 and 0.5 Hz. In addition to accelerating rates of total protein synthesis, electrical stimulation of contraction accelerated fractional rates of synthesis of myosin heavy chain by 42 +/- 8%, P < 0.05. Protein synthesis rates were not accelerated upon electrical stimulation using subthreshold voltages. Addition of 100 ng/ml of actinomycin D had no effect on the ability of electrical stimulation of contraction to accelerate protein synthesis. To uncouple excitation-contraction coupling, 2,3-butanedione monoxime (BDM) was used to block actin-myosin cross-bridge interactions. BDM significantly decreased the ability of electrical stimulation to accelerate protein synthesis rates.

Contraction Accelerates Myosin Heavy Chain Synthesis Rates in Adult Cardiocytes by an Increase in the Rate of Translational Initiation

“…In previous studies employing adult feline cardiocytes in primary culture, we demonstrated that electrically stimulated contraction resulted in an acute acceleration of both total protein synthesis and MHC synthesis rates (6). Two lines of evidence suggested that this acceleration occurred via a mechanism involving an increase in translational activity.…”

“…Electrical Stimulation Model-Adult feline cardiocytes were obtained by collagenase digestion in combination with mechanical agitation as described previously (6,8,9). Following cell isolation, the Ca 2ϩ -tolerant cardiocytes were placed in Life Technologies, Inc. M199 serumfree medium with Earle's salts at a concentration of 50,000 rod-shaped cells/ml.…”

“…After an overnight incubation, the medium was changed to remove nonadherent cells. The M199 medium was modified as before, and adult feline cardiocytes, which are normally quiescent in culture, were induced to contract synchronously via electrical field stimulation as described previously with modification (6). In order to stimulate a larger number of cardiocytes, the system was adapted according to the method of Berger et al (22) for use with large culture trays in which electrical pulses were delivered to the medium via carbon electrodes submersed at the opposite ends of each tray (Fig.…”

“…The specific radioactivity of Phe in the medium was determined by scintillation counting of aliquots of culture medium. Previous studies have shown that the Phe-tRNA pools equilibrate to 80% of medium Phe-specific radioactivity in both electrically stimulated and quiescent cardiocytes (6).…”

“…These findings have been extended to isolated adult cardiocytes in culture. Rates of protein synthesis were accelerated in response to electrically stimulated cardiocyte contraction (6,7), in response to a basal load as defined by adherence of the cardiocytes to the culture dish and establishment of a resting length (8) and in response to passive stretch of cardiocytes adherent to a deformable membrane (9). Thus, the integrity of adult cardiocytes in primary culture is maintained with respect to the ability to transduce changes in mechanical load into an anabolic response such as accelerated protein synthesis rate.…”