Proximal tubule (PT) transports most of the renal Ca

2+

which was usually described as paracellular (passive). We found a regulated Ca

2+

entry pathway in PT cells via the apical transient receptor potential canonical 3 (TRPC3) channel

which initiates transcellular Ca

2+

transport. Although

TRPC3

knockout (−/−) mice were mildly hypercalciuric and displayed luminal calcium phosphate (CaP) crystals at Loop of Henle (LOH)

no CaP + calcium oxalate (CaOx) mixed urine crystals were spotted

which are mostly found in calcium nephrolithiasis (CaNL). Thus

we used oral calcium gluconate (CaG; 2%) to raise the PT luminal [Ca

2+

]

o

further in

TRPC3

−/−

mice for developing such mixed stones to understand the mechanistic role of PT-Ca

2+

signaling in CaNL. Expectedly

CaG-treated mice urine samples presented with numerous mixed crystals with remains of PT cells

which were pronounced in

TRPC3

−/−

mice

indicating PT cell damage. Notably

PT cells from CaG-treated groups switched their mode of Ca

2+

entry from receptor-operated to store-operated pathway with a sustained rise in intracellular [Ca

2+

] ([Ca

2+

]

i

)

indicating the stagnation in PT Ca

2+

transport. Moreover

those PT cells from CaG-treated groups demonstrated an upregulation of calcification

inflammation

fibrotic

oxidative stress

and apoptotic genes; effects of which were more robust in TRPC3 ablated condition. Furthermore

kidneys from CaG-treated groups exhibited fibrosis

tubular injury and calcifications with significant reactive oxygen species generation in the urine

thus

indicating

in vivo

CaNL. Taken together

excess PT luminal Ca

2+

due to escalation of hypercalciuria in TRPC3 ablated mice induced surplus CaP crystal formation and caused stagnation of PT [Ca

2+

]

i

invoking PT cell injury

hence mixed stone formation.