1.Local activation of contraction in isolated rat ventricular myocytes.
O'Neill SC1, Mill JG, Eisner DA. Am J Physiol. 1990 Jun;258(6 Pt 1):C1165-8.
The aim of this paper was to examine whether contraction (which is thought to result from Ca-induced release of Ca2+ from the sarcoplasmic reticulum) can propagate along a cardiac cell. The experiments were performed on isolated rat ventricular cardiac myocytes. Two techniques were used to initiate contraction in a localized region of the cell. 1) The cells were loaded with the "caged" Ca-containing compound nitr-5. A region of the cell was illuminated with ultraviolet light to increase intracellular Ca2+ concentration ([Ca2+]i) in that area. 2) The cells were superfused with a low (0.1 mM) Ca solution to abolish contraction. Ca was applied to a region of the cell by iontophoresis, and the cell was then electrically stimulated. In both cases a local contraction was produced that did not spread to the rest of the cell. Like the normal twitch, the local contraction was abolished by ryanodine, showing that it is produced by Ca release from the sarcoplasmic reticulum.
2.Role of [Ca2+]i in the ATP-induced heat sensitization process of rat nociceptive neurons.
Kress M1, Guenther S. J Neurophysiol. 1999 Jun;81(6):2612-9.
In inflamed tissue, nociceptors show increased sensitivity to noxious heat, which may account for heat hyperalgesia. In unmyelinated nociceptive afferents in rat skin in vitro, a drop of heat threshold and an increase in heat responses were induced by experimental elevation of intracellular calcium ([Ca2+]i) levels with the calcium ionophore ionomycin (10 microM). Similar results were obtained in experiments employing [Ca2+]i release from preloaded "caged calcium" (NITR-5/AM) via UV photolysis. In both cases, sensitization was prevented by preventing rises in [Ca2+]i with the membrane-permeant calcium chelator BAPTA-AM (1 mM). No pronounced change of mechanical sensitivity was observed. Heat-induced membrane currents (Iheat) were investigated with patch-clamp recordings, and simultaneous calcium measurements were performed in small sensory neurons isolated from adult rat dorsal root ganglia (DRG). Ionomycin-induced rises in [Ca2+]i resulted in reversible sensitization of Iheat.
3.The potential signalling pathways which regulate surface changes induced by phytohormones in the potato cyst nematode (Globodera rostochiensis).
Akhkha A1, Curtis R, Kennedy M, Kusel J. Parasitology. 2004 May;128(Pt 5):533-9.
It has been demonstrated that the surface lipophilicity of the plant-parasitic nematode Globodera rostochiensis decreases when infective larvae are exposed to the phytohormones indole-3-acetic acid (auxin) or kinetin (cytokinin). In the present study, it was shown that inhibition of phospholipase C (PLC) or phosphatidylinositol 3 kinase (PI3-kinase) reversed the effect of phytohormones on surface lipophilicity. The signalling pathway(s) involved in surface modification were investigated using 'caged' signalling molecules and stimulators or inhibitors of different signalling enzymes. Photolysis of the 'caged' signalling molecules, NPE-caged Ins 1,4,5-P3, NITR-5/AM or caged-cAMP to liberate IP3, Ca2+ or cAMP respectively, decreased the surface lipophilicity. Activation of adenylate cyclase also decreased the surface lipophilicity. In contrast, inhibition of PI3-kinase using Wortmannin, LY-294002 or Quercetin, and inhibition of PLC using U-73122 all increased the surface lipophilicity.
4.The effect of caged calcium release on the adaptation of the transduction current in chick hair cells.
Kimitsuki T1, Ohmori H. J Physiol. 1992 Dec;458:27-40.
1. Intracellular Ca2+ concentration ([Ca2+]i) was raised by photolysis of a caged calcium compound, nitr-5, and its effects on the mechano-electrical transduction (MET) current were studied by a whole-cell patch electrode voltage clamp technique in dissociated hair cells of a chick. Nitr-5 was loaded into the hair cell by incubation with the membrane-permeable form of the compound (nitr-5 AM). 2. Photolysis of nitr-5 by ultraviolet (UV) light irradiation induced outward currents at -50 mV when recorded with a KCl-based intracellular medium without Ca2+ chelating compounds. The average amplitude of the photo-activated outward current was 115 +/- 82 pA (mean +/- S.D., n = 5). 3. The MET current generated at -50 mV showed a decay after step displacement of the hair bundle. This adaptation was accelerated after UV exposure of the cell. The adaptation was further accelerated by hyperpolarization of the membrane and was eliminated in 20-100 microM Ca2+ extracellular media.