Cellular Responses to Metal Ions Released From Implants

In the process of calcified tissue formation, cells secrete a protein-rich matrix into which they add a metal ion that nucleates in the presence of phosphorus to form an inorganic salt (usually calcium hydroxyapatite). Cellular and tissue responses to metal ions—released from implants, for example—can therefore be considered from the perspective of how cells handle calcium ions. A critical factor in determining cellular toxicity will be free ion concentrations and the competitive interactions that occur in a physicochemical manner. Three of the parameters used to assess the biocompatibility of implant materials are (1) the ability to influence mitotic activity, (2) intercellular adhesion, and (3) promotion of cell death. A spectrum of responses to free intracellular calcium ions can be identified, ranging from presence of the ion being essential for cell division through to an excess of the free ion that results in cell death (apoptosis). In between these extremes, cells may become postmitotic and express phenotypic variations as they adapt to their environment and establish equilibrium to maintain intracellular calcium homeostasis. The response of cells to implants can be linked to ions released and interactions between these and other ions and/or molecules present in the tissues, similar to the manner in which cells handle calcium ions.

Mechanisms underlying oocyte activation and postovulatory ageing

Mammalian oocytes undergo significant growth during oogenesis and experience extensive cytoplasmic and nuclear modifications immediately before ovulation in a process commonly referred to as oocyte maturation. These changes are intended to maximize the developmental success after fertilization. Entry of a spermatozoon into the oocyte, which occurs a few hours after ovulation, initiates long-lasting oscillations in the free intracellular calcium ([Ca(2+)](i)) that are responsible for all events of oocyte activation and the initiation of the developmental programme that often culminates in the birth of young. Nevertheless, the cellular and molecular changes that occur during maturation to optimize development are transient, and exhibit rapid deterioration. Moreover, fertilization of oocytes after an extended residence in the oviduct (or in culture) initiates a different developmental programme, one that is characterized by fragmentation, programmed cell death, and abnormal development. Inasmuch as [Ca(2+)](i) oscillations can trigger both developmental programmes in mammalian oocytes, this review addresses one of the mechanism(s) possibly used by spermatozoa to initiate these persistent [Ca(2+)](i) responses, and the cellular and molecular changes that may underlie the postovulatory cellular fragmentation of ageing mammalian oocytes.

Acetylcholine Increases the Free Intracellular Calcium Concentration in Podocytes in Intact Rat Glomeruli via Muscarinic M5 Receptors

The effects of acetylcholine (ACh) on the free intracellular calcium concentration ([Ca2+]i) of microdissected glomeruli were investigated using fura-2 fluorescence digital imaging and two-photon confocal microscopy. ACh caused a concentration-dependent [Ca2+]i increases with an initial peak followed by a sustained plateau, which was suppressed by reduced extracellular Ca2+ concentrations. The [Ca2+]i plateau was not affected by the L-type Ca2+ channel blocker nicardipine, whereas gadolinium and lanthanum (both at 1 μM) blocked the plateau. Diphenylacetoxy-N-methylpiperidine methiodide (100 nM), an M3/M5 receptor antagonist, and pirenzepine (1 μM), an M1 receptor antagonist, completely inhibited the effect of ACh. [Ca2+]i measurements using two-photon excitation of fluo-3 and staining of the cells with calcein/acetoxymethyl ester, for observation of the capillary network together with the glomerular cells, showed that [Ca2+]i was increased in single podocytes. Immunohistochemical studies did not demonstrate M3 receptor expression in glomerular cells. M1 receptors could be detected only in the parietal sheet of Bowman's capsule, whereas M5 receptors were found only in podocytes. The data show that ACh increases [Ca2+]i in podocytes of intact glomeruli, most likely via muscarinic M5 receptors.

Simultaneous arterial calcium dynamics and diameter measurements: application to myoendothelial communication

The goal of the present study was to analyze the intercellular calcium communication between smooth muscle cells (SMCs) and endothelial cells (ECs) by simultaneously monitoring artery diameter and intracellular calcium concentration in a rat mesenteric arterial segment in vitro under physiological pressure (50 mmHg) and flow (50 μl/min) in a specially developed system. Intracellular calcium was expressed as the fura 2 ratio. The diameter was measured using a digital image acquisition system. Stimulation of SMCs with the α1-agonist phenylephrine (PE) caused not only an increase in the free intracellular calcium concentration of the SMCs as expected but also in the ECs, suggesting a calcium flux from the SMCs to the ECs. The gap junction uncoupler palmitoleic acid greatly reduced this increase in calcium in the ECs on stimulation of the SMCs with PE. This indicates that the signaling pathway passes through the gap junctions. Similarly, although vasomotion originates in the SMCs, calcium oscillates in both SMCs and ECs during vasomotion, suggesting again a calcium flux from the SMCs to the ECs.