Electrophysiology of single cardiac cells.

Abstract

The importance of using single myocytes isolated from the adult mammalian heart has lately received wide recognition, and many investigations on ionic currents using single ventricular cells have appeared from various laboratories. Cultured myocytes isolated from embryonic hearts have been a matter of interest for a long time, especially from a developmental standpoint, but their sizes are so small that most of the electrophysiological studies have been conducted on sheet, strand, or cluster specimens. In 1969, KoNO [31] isolated single adult rat ventricular cells through the collagenase treatment; since then many methods for preparing viable cardiac cells have been reported, but few physiological studies were done using these single cells until POWELL, TERRAR, and TWIST [49, 50] and ISENBERG and KLOCKNER [21] demonstrated the usefulness of the single cell for physiological study.The heart has a functional synticytium and the excitation of a single cell is conducted to the adjacent cells through low resistance nexus [64]. Much traditional electrophysiological work on heart muscle has been carried out with multicellular muscle strands, such as Purkinje fibers and the papillary strands. Using these preparations, most basic properties of excitation and conduction of the heart muscle have been established. Voltage clamp experiments in multicellular specimens [for review, see Refs. 4,9,42] are not ideal because of the difficulty of the spatial clamp and the desire of most cardiac physiologists to design their experiments using single cardiac cells. Thus the work of POWELL and TWIST [50] stimulated researchers in many fields of cardiac electrophysiology to develop a method of obtaining viable cardiac cells and to devise a way of recording electrical activity from single cells.Another development which triggered single cell physiology was the introduction of the patch clamp method [14], where single ionic channel activity and statistical analyses of channel activity became available. This newly developed method in the electrophysiology of the cardiac cell spurred increased interest among general physiologists and biophysicists, as well as cardiac physiologists.Single myocytes isolated from the adult heart have the following unique features.

Voltage clamp of bull‐frog cardiac pace‐maker cells: a quantitative analysis of potassium currents.

“…node (cf. Irisawa, 1984). In the majority of these preparations two K+-conductance The I-V relationship observed for the fully activated 'K current is approximately linear.…”

“…node tissue by Irisawa and his colleagues (cf. Irisawa, 1984). The mammalian cells are spontaneously active and generate substantial action potentials.…”

“…Yanagihara & Irisawa, 1980;DiFrancesco, 1981) and single cells derived from the rabbit s.a. node (cf. Irisawa, 1984;Maylie & Morad, 1984;van Ginneken & Giles, 1985) and single myocytes from sheep or dog Purkinje tissue (Callewaert, Carmeliet, van der Heyden & Vereecke, 1982). Interestingly, however, in spontaneously pacing…”

“…nodes (cf. Irisawa, 1984) and the bull-frog sinus venosus (Shibata & Giles, 1983). Data obtained by Noma, Irisawa, and their colleagues (cf.…”

Voltage clamp measurements of the hyperpolarization‐activated inward current I(f) in single cells from rabbit sino‐atrial node.

“…Nakayama et al (1984) and DiFrancesco et al (1986) A. C G. VAN I-V relation of r in iisolated S-A node cells Since the inwardly rectifying K+ current IK1' is very small or absent in cells from the S-A node Irisawa, 1984), the instantaneous 1-V relation of I can be obtained without interference from other currents. Typical raw I-V data (panel A) and an instantaneous I-V relationship (panel B) are shown in Fig.…”