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2 Department of Pharmacology and Physiology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103
3 Department of Biomedical Sciences, University of Padua, 35121 Padua, Italy
Address correspondence to to Célia R.S. Garcia, Department of Physiology, Institute of Biosciences, University of São Paulo, Rua do Matão, travessa 14, n321, São Paulo 05508-900, Brazil. Tel.: 5511-30917518. Fax: 5511-30917422. E-mail: cgarcia{at}usp.br
Malaria parasites, Plasmodia, spend most of their asexual life cycle within red blood cells, where they proliferate and mature. The erythrocyte cytoplasm has very low [Ca2+] (<100 nM), which is very different from the extracellular environment encountered by most eukaryotic cells. The absence of extracellular Ca2+ is usually incompatible with normal cell functions and survival. In the present work, we have tested the possibility that Plasmodia overcome the limitation posed by the erythrocyte intracellular environment through the maintenance of a high [Ca2+] within the parasitophorous vacuole (PV), the compartment formed during invasion and within which the parasites grow and divide. Thus, Plasmodia were allowed to invade erythrocytes in the presence of Ca2+ indicator dyes. This allowed selective loading of the Ca2+ probes within the PV. The [Ca2+] within this compartment was found to be
40 µM, i.e., high enough to be compatible with a normal loading of the Plasmodia intracellular Ca2+ stores, a prerequisite for the use of a Ca2+-based signaling mechanism. We also show that reduction of extracellular [Ca2+] results in a slow depletion of the [Ca2+] within the PV. A transient drop of [Ca2+] in the PV for a period as short as 2 h affects the maturation process of the parasites within the erythrocytes, with a major reduction 48 h later in the percentage of schizonts, the form that re-invades the red blood cells.
Key Words: parasitophorous vacuole; signal transduction; Plasmodium; calcium indicators; melatonin
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