Gap junction-mediated intercellular diffusion of Ca2+ in cultured human corporal smooth muscle cells

Abstract

Ratio imaging using the calcium-sensitive probe fura-2 was employed to study intracellular calcium concentrations and intercellular calcium flux through gap junctions in homogeneous vascular smooth muscle cell cultures derived from the human corpora cavernosa. Microinjection techniques demonstrated that fura-2 free acid was freely diffusible through gap junctions between cultured cells. The resting intracellular calcium level in fura-2-loaded cells was 176.9 +/- 10.5. A robust increase in intracellular calcium was seen in response to both phenylephrine and the calcium ionophore A23187. Microinjection of Ca2+ into individual smooth muscle cells always resulted in significant, although temporally delayed, increases in intracellular calcium levels in adjacent cells; this intercellular calcium flux was reversibly blocked by inhibition of gap junctional communication with 2 mM heptanol. However, although microinjection of D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] into individual smooth muscle cells always produced significant increases in intracellular calcium levels in the injected cell, the intercellular spread of Ca2+ in response to Ins(1,4,5)P3 was more variable than for Ca2+ injections. These studies demonstrate that Ca2+, and perhaps Ins(1,4,5)P3 as well, can diffuse between smooth muscle cells through gap junction channels.

Gap junctions in isolated rat aorta: evidence for contractile responses that exhibit a differential dependence on intercellular communication

“…Furthermore, for any given level of myosin phosphorylation, ET-1-induced contractile responses are associated with the greater levels of tension development. In this context, such observations are consistent with the supposition that intercellular calcium/IP 3 diffusion may be a primary mechanism for propagating/coordinating vascular smooth muscle responses (15). Therefore, there are several independent lines of investigation that support the hypothesis that ET-1-induced contractions, by virtue of the apparently greater cellular sensitivity their activation invokes, may be more gap junction independent than contractions of equivalent magnitude produced by other agonists.…”

“…The implication of such observations is that another mechanism is required for the coordination of vasomotor tone. In this regard, aqueous intercellular channels, referred to as gap junctions, are known to interconnect adjacent cells in most tissues including vascular smooth muscle (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Gap junctions provide partial cytoplasmic continuity between coupled cells, and thus serve as an ideal anatomic substrate for coordinating tissue responses (5,13,19).…”

Calcium permeability of the neuronal nuclear envelope: evaluation using confocal volumes and intracellular perfusion

“…More recent studies using fluorescent dextrans arrive at the same conclusion and show that dextrans with molecular weights up to 17,000 Da can rapidly cross the nuclear membrane (Peters, 1984(Peters, , 1986Lang et al, 1986). Increased nuclear fluorescence is also observed with the charged form of ratiometric dyes (Neylon et al, 1990;Christ et al, 1992;Glennon et al, 1992;Neher and Augustine, 1992).…”

Connexin channel permeability to cytoplasmic molecules

“…In some cases, it is clear that regenerative Ca signaling is mediated by IP3 flux and that the contribution of junctional Ca flux to this process is minor (Venance et al, 1997;Leybaert et al, 1998). In other cases it appears that junctional Ca flux is a major factor (Sáez et al, 1989;Boitano et al, 1992;Christ et al, 1992). Computational modeling has supported both scenarios, and delineated synergistic roles for both (Sneyd et al, 1994;Sneyd et al, 1998;Höfer, 1999;Höfer et al 2001;Höfer et al, 2002;Iacobas et al, 2006).…”

“…Ca++ (Christ et al, 1992) 1a 2 5 38h ATP (Bahima et al, 2006) 3a 3b 3c 43h ATP (Cotrina et al, 1998) 3a 3b 3c (connexin block had only partial effect)…”