Fast calcium wave propagation mediated by electrically conducted excitation and boosted by CICR

Abstract

Kusters JM, van Meerwijk WP, Ypey DL, Theuvenet AP, Gielen CC. Fast calcium wave propagation mediated by electrically conducted excitation and boosted by CICR. Am J Physiol Cell Physiol 294: C917-C930, 2008. First published January 16, 2008 doi:10.1152/ajpcell.00181.2007.-We have investigated synchronization and propagation of calcium oscillations, mediated by gap junctional excitation transmission. For that purpose we used an experimentally based model of normal rat kidney (NRK) cells, electrically coupled in a one-dimensional configuration (linear strand). Fibroblasts such as NRK cells can form an excitable syncytium and generate spontaneous inositol 1,4,5-trisphosphate (IP3)-mediated intracellular calcium waves, which may spread over a monolayer culture in a coordinated fashion. An intracellular calcium oscillation in a pacemaker cell causes a membrane depolarization from within that cell via calcium-activated chloride channels, leading to an L-type calcium channel-based action potential (AP) in that cell. This AP is then transmitted to the electrically connected neighbor cell, and the calcium inflow during that transmitted AP triggers a calcium wave in that neighbor cell by opening of IP3 receptor channels, causing calciuminduced calcium release (CICR). In this way the calcium wave of the pacemaker cell is rapidly propagated by the electrically transmitted AP. Propagation of APs in a strand of cells depends on the number of terminal pacemaker cells, the L-type calcium conductance of the cells, and the electrical coupling between the cells. Our results show that the coupling between IP3-mediated calcium oscillations and AP firing provides a robust mechanism for fast propagation of activity across a network of cells, which is representative for many other cell types such as gastrointestinal cells, urethral cells, and pacemaker cells in the heart. gap junctions; calcium waves; pacemaking; electrical coupling; action potential propagation; inositol 1,4,5-trisphosphate receptor; normal rat kidney cell; calcium-induced calcium release INTRACELLULAR CALCIUM OSCILLATIONS are very common and have been reported in a large variety of cell types, such as smooth muscle cells (39), hepatocytes (47), oocytes (5), normal rat kidney (NRK) fibroblast cells (16), and pancreatic acinar cells (11,33). In these cell types, the cytosolic calcium transients are evoked by inositol 1,4,5-trisphosphate (IP 3 )-linked agonist stimulation: after interacting with cell-surface receptors, agonists activate phospholipase C and induce the release of IP 3 . IP 3 then triggers calcium release from intracellular stores through IP 3 -sensitive calcium release channels in the endoplasmic reticulum (ER) membrane (32). Calcium liberation from the ER can also be activated by cytosolic calcium in the presence of IP 3 . In our model, the main mechanism of calcium-induced calcium release (CICR) is the opening of the IP 3 receptor (but other release mechanisms of intracellular calcium may do as well).In the cell types mentioned above, the cells are con...

Spontaneous Ca2+ Waves in Rabbit Corpus Cavernosum: Modulation by Nitric Oxide and cGMP

“…They were also blocked by agents that interfere with IP 3 R (2-APB and NCDC) or RyR (tetracaine), suggesting that cooperative activity of both types of Ca 2+ release channel was necessary for propagating Ca 2+ waves to occur. A helpful mathematical model has recently described the relationships between a pacemaker mechanism involving intracellular Ca 2+ release, followed by depolarization mediated by Clchannels, followed by wave propagation mediated by electrical conduction through gap junctions and boosted by Ca 2+ -induced Ca 2+ release, in monolayers of cultured excitable kidney fibroblasts [25]. The results of the present study, taken together with evidence of gap junctions [26], suggest that all of the necessary elements are present for a similar mechanism to be possible in the corpus cavernosum.…”

Local induction of pacemaking activity in a monolayer of electrically coupled quiescent NRK fibroblasts

“…Mathematical modeling: Computer simulations were per formed using the mathematical model of normal rat kidney (NRK) fibroblasts reported in previous studies [18][19][20]. Each cell in the model consists of two compartments: a single calcium store, located in the endoplasmic reticulum (ER), and the cytosol.…”

“…The model describes the dynamics of the membrane potential, the transmembrane currents and the intracellular calcium oscillator, based on a coupling between the kinet ics of the excitable membrane and that of the intracellular calcium oscillator by cytosolic calcium [19]. Moreover, the model explains the generation and propagation of repetitive action potentials and calcium waves in a one-dimensional network of NRK cells [20]. Details of the model and the parameter values used in the simulations have been pre sented previously [19,20].…”

Complex life forms may arise from electrical processes

“…In this case a chemically mediated process, the application of ET-1, caused enhanced synthesis of IP 3 which caused Ca 2+ store release into the cytoplasm which then led to global synchronous Ca 2+ transients associated with action potentials. Kusters et al [20], using the NRK system of fibroblasts, emphasized that the rapid calcium wave propagation is "boosted" by calcium-induced calcium release (CICR). IP 3 -mediated calcium oscillation and action potential generation couple with each other, producing very robust pacemakers for propagating signals through the cell network.…”